I've got 3500 miles on my 05 duramax. My fuel economy seems to be way off of what my 03 did. My brother bought an 05 at the same time I did. He is averaging at a minimum 18mpg. I can get above 16. I have put 265 all terrian tire on my though. These were taken off of my 03. Any thoughts or nothing to worry about. My current tank with no towing and mixture of highway and city I'm averaging 15mpg.

Thanks

Seems a little low but the tires might be making a difference. I average 16 to 17 with mostly in town driving. Also, I don't put my foot into it very often either.

Are you correcting your miles traveled for the different size tires? I believe that you can have the dealer program your truck to have correct speedo and odometer readings for the 265s. My truck is a 3500 and comes with 265s.

jeff

I have been reading the forum for about 5 months now and am having a hard time believing the mileage claims I am reading. I have a bone stock 2500 silverado HD, Allison automatic, 4wd, 389 rear end and the best I can get unloaded with cruise control set at 70 on interstate is 15.5. I can get about 18 with cruise set at 55. My truck has 11,500 mi. on it.

I have 285's on mine (speedo corrected with programmer) simi-freeway I get 18 ish, around town it's 16, and towing my toy hauler (depending how loaded it is) I get 9 to 11. I haven't run an entire tank on the freeway (unloaded) so I don't have that #. O'ya; I have 9k on the odometer and it is very flat around here.

I changed from BFG MT (265s) to Goodyear Wrangler ATS (265s, E) and picked up about 1.5 mpg and quieted down the tire noise quite a bit, too. There's a web link here someplace for a means to figure out speedo differences generated w/tire size changes from OEM. When I tried it out, I found about a 4 mph difference when going from the stock 245s to 265/75R/16. For example, when your speedo reads 60 mph, you'll actually be going 64 mph; when you odometer clocks 100K miles, it will actually have 104K miles...

My neighbor and I bought identical 05s a month ago. We both put 265s on. I also put a 4" exhaust on - he didn't. I also have the predator @ 65. I get 19.7 mixed mode driving (city / hwy). He gets 15. We have both calculated this by hand and have found the DIC is pretty accurate. We both get gas at the same place.
I find it hard to believe that my exhaust give me the edge. From reading the forums I see that the stats are all over the place. Go figure.

I actually checked my speedo with gps on a trip. I was within a mile per hour. The thing that makes me wonder is why my 03 got 3 mpg better with the same setup. Might put stock tires on a see what happens.

I have been reading the forum for about 5 months now and am having a hard time believing the mileage claims I am reading. I have a bone stock 2500 silverado HD, Allison automatic, 4wd, 389 rear end and the best I can get unloaded with cruise control set at 70 on interstate is 15.5. I can get about 18 with cruise set at 55. My truck has 11,500 mi. on it.

Ask the dealer to do a reflash. With that kind of milage there has to be something wrong. With cruise at 70 on HWY I see avg 20 mpg.

I have the same gripe. I had an 03 that did much better in mileage, both towing and un hitched.
The 03 would consistantly get 17-19 pure highway
About 9-10 towing 10,000 pounds,
And 13-15 Mixed.
I hated it then, but NOW!!!!!!
My 2005 gets at best 14.5 on the HIGHWAY, no foot in it 70mph.
TOWING forget it. Same trailer, and the best I EVER did was 8.5.
I can truly say, I hate the truck for this. All I ever heard was more power, better mileage. BULL . People here either luv their trucks they are dilusional about their mileage claims or really Believe the DIC readings. or I am just one of the 'few' unlucky suckers that got a Mileage lemon.

ALSO, the 05 claims more HP, and my pulling power with the 03 was at least 5 MPH better over familiar grades. SO, it's enough to make me look hard at a gasser next time around. I hate to say it, but I've gone negative on Dmax.

Even tried a programmer (Predator) to get some better numbers. A bunch of smoke and NO luck at all on MPG's but nice power increases!

Sorry to be so negative, but I paid a fortune for a truck that hasn'e quite met my expectations, and I find it hard to dump in a bunch of "add ons" to get it where it should just be. I guess I am not a 'purist' truck luver!

Tried the additives Primrose and some other 'trusted' brands. No change.

Although maybe it is temporary, but here in California, I pay almost as much for Diesel as the guy filling up his Corvette (premium). And I am putting fuel-oil in my vehicle? BULL SHEIT May as well be driving a gasser then. Gonna trade every 5 years anyways. So, it's not about a marriage or miles driven.

ANY suggestions to get me back in camp? I do wanna LUV my truck guys. But I think we need counseling!!!!

THANKS!!!

. People here either luv their trucks they are dilusional about their mileage claims or really Believe the DIC readings.

I am not dilusional about my mileage, and I don't even use my DIC because the predator throws it off big time. I DO GET 21mpg @ 72ish mph cruise and a/c on and this is hand calculated and fuel filled to the same spot every time. Maybe the EGR block off, my catless front pipe, and the predator helped me, because when it was new I was getting about 18mpg hwy.

So far, hand calculated, I have gotten around 15.9 mpg and I usually only drive in town 5 miles to and from work and little (less then 10 miles highway per tank), at work a lot of driving back and forth between buildings. The killer was my last tank of fuel, I got 13.77 mpg and that was with a lot of idling invovled. The best I got was 18.5 mixed about 60% in town 40% highway. A lot of it really has to do with how you drive (read right foot) and where you drive. My buddy has an 05 Gmc2500 reg cab long bed and with about 1500lbs equipment in back gets about 17.5 mpg mixed driving. FWIW

I am not dilusional about my mileage, and I don't even use my DIC because the predator throws it off big time. I DO GET 21mpg @ 72ish mph cruise and a/c on and this is hand calculated and fuel filled to the same spot every time. Maybe the EGR block off, my catless front pipe, and the predator helped me, because when it was new I was getting about 18mpg hwy.

Well, I envy you. And I should have said 'some' dilusional folks!

As I said, I owned an 03 and a 05, both of which the DICs were worthless, whether tuned or not. But I think many of these guys here do rely on the DIC to quote mileage. And that IS a joke. YOU seem to have 'scored' with your truck, and setup, since your mileage calcs are real obviously.

But you have those who can add and subtract, and you have those who rely on the "Computer".

I just wish I was even near your 'camp' when it comes to those figures. I could put a :) on my face then.

The reality is the numbers are all over the place. The hard thing to figure is that the engines are built to strict tolerances, and driving habits and geography would play a certain part in it all, but

The best I can get on my 05 is 17.5 mostly hiway. Has anybody reflashed and improved their mileage, let us hear from you.

I have been reading the forum for about 5 months now and am having a hard time believing the mileage claims I am reading. I have a bone stock 2500 silverado HD, Allison automatic, 4wd, 389 rear end and the best I can get unloaded with cruise control set at 70 on interstate is 15.5. I can get about 18 with cruise set at 55. My truck has 11,500 mi. on it.

I'm pretty sure stock gears are 3.73, but I agree MPG's for the stock '05's bite..I was getting about 15.5 50/50 driving. Now woth Predator @ 65hp, AFE Intake, I'm getting low 16's. I'm getting exhaust, fingers, EGR blocker Plate installed this weekend. We'll see.

Kudos, to all the stockers getting 20+mph, is that consistent or the best you've gotten? I know on my old '01 D/A I got 21.7 mpg once up North. But at sea level, where I am, I was getting 17.

Just as another data point... totally stock here. With a heavy-ish foot (revs to about 2600 rpm between shifts) and 50/50 city/highway mix, I get about 16 to 16.5 (about .5 less during the winter). Driving easy (seldom revving past 2K) on that same 50/50 city/highway mix keeping highway speeds around 60, I get in the high 18s to low 19s. I haven't taken an all highway trip with it yet so can't comment on pure highway mileage. I fill to the same point on the filler neck every time and hand calculate.

I've got just over 10K miles on it now and have not really noticed any increase in mileage since it was new. I have the original early 05 PCM settings (no reflash - I took delivery before the reflash was available and haven't been back to the dealer since). No surges, stumbles or smoke.

I think the variables are in the manufacturing. A "build up in tolerances". Much like the over heaters. If you end up with a high percentage of controls and parts on the edge of their tolerances you get poor results. I had two 04.5 trucks, one got 18 mpg, and one got 15. I now have two 05's, one gets 18 best, the other gets 20 best. The ones that get the better fuel mileage are also the ones that run the best.

Totally stock with less that 1200 mils on odo, I get 15.3 in 50/50 city/high way driving but I got close to 20 on 600 mile high way driving at 65-70 Mph. I claculated by hand. I never trusted DIC.

I'm not dilusional either, my 05 got 18.5 mpg Hand Calculated going over a 5500ft mountain pass & back for a 400 mile trip & 18.7 on the DIC. I hit 90mpg on uphill passes. MPH averaged 70 on highway & 50-60 in the curvy mountain pass areas.

from the reports i've read, the DIC on the 05's stock seem to be very accurate. Mine has been exactly right to .2 - .3 off max.

havent done any heavy towing yet. mpg seemed to improve on the trip to be honest. we were only getting 17.5 average until the trip. now were averaging 18 to work & back with mostly highway driving.

However, a friend of mine hasnt gotten his DIC to read 15mpg yet!!! makes me wonder about break in. because thats what mine was getting on the 1st tank.

bill

Well, I envy you. And I should have said 'some' dilusional folks!

As I said, I owned an 03 and a 05, both of which the DICs were worthless, whether tuned or not. But I think many of these guys here do rely on the DIC to quote mileage. And that IS a joke. YOU seem to have 'scored' with your truck, and setup, since your mileage calcs are real obviously.

But you have those who can add and subtract, and you have those who rely on the "Computer".

I just wish I was even near your 'camp' when it comes to those figures. I could put a :) on my face then.

The reality is the numbers are all over the place. The hard thing to figure is that the engines are built to strict tolerances, and driving habits and geography would play a certain part in it all, but

I have been reading the forum for about 5 months now and am having a hard time believing the mileage claims I am reading. I have a bone stock 2500 silverado HD, Allison automatic, 4wd, 389 rear end and the best I can get unloaded with cruise control set at 70 on interstate is 15.5. I can get about 18 with cruise set at 55. My truck has 11,500 mi. on it.

Is your 389 rear end custom? All I've seen from the factory is 3.73 and 4.10.
I have the 3.73 in an 05 Longbed Crew Cab. At 70, I'm getting 20+. I did a test tonite: Cruising 55mph, reset the Avg Fuel Econ and drove for 5 miles. The DIC indicated an average of 25.4 mpg. Unfortunately I don't drive 55 very often. My truck is stock with only 1400 miles on it. Around town and adding in a little freeway driving, I average 15.

Dave

I have a 05 CC LB, completely stock until yesterday. The only change I have made is adding a bedcover. My millage has been consistant at 16 to 17 MPG combined city and highway. Yesterday I installed a Snug Top Bedcover and did some testing by resetting the DIC millage calculator while driving on a level section of highway. My Millage before snug top was as stated above when I did this, this test however it showed 21 to 22. (at 65MPH).

I have only put 100 miles on it so far, so time will tell for sure if this is going to be my overall results. My thoughts however are that I will see some increase due to the loss of drag from the tailgate. I will keep you all posted over the next couple weeks.

I would be interesting to take a poll of millage differences LB vs SB, CC, vs other cabs and so on. I understand that a heavy foot will decrease, and I do have a hit of a heavy foot so I will never get good millage in town. I have to live with my heavy foot in town and take a loss in millage.

Something for everyone to think about tho.......

John

The amount mileage varies in these trucks amazes me.
I guess I'll have to be happy I got a good one.

I'm getting 20-21 consistantly as a daily driver (hand calculated). The DIC is usually within a half mpg with calculated figures.
Mileage does DROP pulling my 5er though. Got 11.5 on a 400 mile tow last week across Ohio. I was surpised how much the trailer drops it, but my last truck had a 8.1 gasser. It only got 5-6 towing. Makes 11.5 look good!!

1st diesel, 5500 mile on the truck, so far I'm impressed to say the least.

My mileage sucked until I hooked up my 25' enclosed car hauler with car, tools, gear, etc.... read HEAVY! I then pulled from Paola, KS. to Bowling Green, KY. hauling ass at some points. In other words, I was running like I ganked the truck/trailer! When I came back mileage was up significantly. Pre-Trip = 12-13 mpg Post-Trip = 15-16 mpg. My rig is a 3500 DRW, CC, Duramax/Alison, 4x4 with approximately 5500 miles on the clock. Currently the only mods are a Predator on 65hp and no muffler....I have a 4" cat-less downpipe on the way. On a flat unloaded run @ 70mph I can see 19-20 mpg no problem on summer fuel.

Forget the MPG's. I JUST PAID $2.999 FOR DIESEL FUEL.

Can someone help me UNDERSTAND how it is possible for the guy next to me filling up his Mercedes with Premium, is paying 25 cents LESSSSSSS than me gallon?
Is it just CALIFORNIA, the land of being screwed? OR everywhere?

What is happening? The argument for a diesel is dwindling....

I am not dilusional about my mileage, and I don't even use my DIC because the predator throws it off big time. I DO GET 21mpg @ 72ish mph cruise and a/c on and this is hand calculated and fuel filled to the same spot every time. Maybe the EGR block off, my catless front pipe, and the predator helped me, because when it was new I was getting about 18mpg hwy.
My set up is close to yours, I have the predator, my EGR is not blocked off, I still have the cat intack however, I do have the MBRP cool duals on my truck.
Before installing the predator, running with the four inch dual pipes my truck empty was getting on the road milage 19-20 mpg @ 70 mph, hand calulated. With predator it will get 20-21.7 mpg, under the same conditions.

EZ set on 30 on "hilly" trip doing 70-75 mph,18mpg. Around town 17-19mpg(all hand calculated).

I have a 2004.5 LLY 2500HD. My truck's DIC life average is 12.4. I do not have a lead foot. When pulling my trailer, which is not often I get low 11's. On the highway it gets high 14's or low 15's. I have Edge w/ Attitude, TrueFlow intake, Roll n' Lock cover, and slightly bigger tires. I was told that the LLY would get better mileage than the LB7, but I have three friends with 2003 or newer LB7's and they average 16.4. I have seen their DIC's.
The only thing I do not have is exhaust. Since nothing has made a difference I find it hard to dump another $600 or $700 into the truck. I have read numerous posts and have too seen astronmical numbers for MPG (compared to mine). Should I take it to the dealer? Can anyone give any suggestions? I keep looking for some magical reason that I get 4 to 5 MPG's less than average. With gas prices so high, that 100 miles a tank is a huge difference. Help!!!

how many miles bthompson just wait out of the blue your miles will just change thats what mine did. i started to doubt what everyone said they were gettng for mpg then mine changed from 15.5 to 17.5 now i'm getting 18.5 t0 20.2 this all happen in 3 weeks time and i only have 2200 miles on it. when i hit 19.7 i took a pic of it i was so happy lol. it's the little things in life that makes us happy i guess :rockit:

Let me start off saying I am brand new to this forum. I traded my 01 8.1 gas dually for a brand spanking ne 05 crew cab dually. I am cosistantly getting 15.2 with the cruise set at 70. In town low 14's to high 13's. looking to increase milage I had a "areo turbine 4040L" muffler installed and as well had the cat cut out and strait pipe installed.Now here's where it gets interesting. Upon leaving the muffler shop heading back to my shop the milage jumped to 19.4 with the cruise set on 70 and that treck covered about 15 miles of highway . I got to my shop and the truck sat for about 2 hours and then I left to make sales calls which was all over the D/FW area. I noticed with the cruise on my milage went to about 15.5 at 70 with the cruise on . I can't figure that one out how it would jump so high then come right back down. There is also something else , now i have this smell around the truck and inside. It's almost like a exaust leak getting in the AC .I checked the strait pipe where the cat was but the welds are really good and not leaking. Oh i have about 7500miles on the truck and about 300 with the new exaust. Any help or opinions would be much appreciated. Thanks

well you will smell more diesel smell with the new exhaust i just put my exhaust on today and i can smell it now also the old big muffler was like a filter and so was the cat.as for the mileage i was getting the same before the exhaust and really no change with the exhaust. on your next fill up reset your dic and see what you get first

I just got mine and it had 5900 miles on it (dealer demo).........I have put about 600 miles on it so far . When I got it the DIC said 15.5 mpg ..........getting on it a lot it dropped to 15 mpg...........took a trip this weekend and took it easy.......average is back up to 15.4 mpg !! Majority of this is city driving ! It's bettter than my 5.3 liter Z-71 so I am happy........but I am not sure if it'll get better than 15-16 mpg around town !

the diesel smell is al around the cab. When I stop at red lights it can get bad enough to bother my eyes inside the cab with the ac on and windows up.

Sorry....I forgot to mention that I had 18,000 miles on my 2004.5 LLY. I appreciate your outlook chp777, but mine has never, ever, gotten 15.5mpg. I consistently get 12 or 12.1 around town. When I say that I am a slow driver, I mean it. I have all of the add-ons and do not hot rod around. I am really disappointed in my gas mileage. It is even more discouraging when I see all of the 16-20's mpgs that have been posted and I have seen with my own eyes. I do not know what else I can do. Could there be something in the manufacturing that could change my mileage that much.

My 05 now has 11,000 miles on it, I had the reflash done to fix the surging problem.

I drive with a really light foot!

Milage around town driving is 13-14mpg.
Freeway is 16-17mpg.

Last weekend going to San Diego got 18.1 going down, all freeway driving.

Coming back, got 16.2 MPG

The real diffrence seems to be if you drive much city driving it really seems to kill over all milage.

Bone stock, except put a snug top camper shell, whick I thoght would help with the milage.

I think the re-flash made it get worse milage than before.

Bone stock, except put a snug top camper shell, whick I thoght would help with the milage.

Everything I have seen shows that a camper shell will reduce mileage. I was also told that removing/dropping your tailgate will reduce mileage as well. I haven't seen anything about the effects a tonneau cover will have, if any.

Joseph

My cap boasted mileage by almost 2 mpg. I noticed the difference right away.
City driving gets my 14.5-16, all hwy gets 18-19 at 65mph, mixed gets 16-16.5. Thats driving at startup very slow not exceeding 2000 rpms and coasting as much as possible into the red lights hoping for green. Hwy towing trailer last trip got 12.5 pulling 4000 lbs at 72 mph. I did just order a removable air deflector for the roof when trailering. I hope it works.

Jeff,

I noticed that you pulled a load very similar to what I had this last weekend, with similar MPG numbers, but you drove faster than I did (I kept it down to ~62 MPH, and got ~12.3 MPG with a 4000# TT). I also noticed that your signature mentions the Aero-Turbine 4040L. Did you notice much of a change in performance/mileage with this mod? Are you using the stock pipes, and adapting up to the 4" required, or did you add in a different set of pipes?

Thanks,

Joseph

I actually checked my speedo with gps on a trip. I was within a mile per hour. The thing that makes me wonder is why my 03 got 3 mpg better with the same setup. Might put stock tires on a see what happens.

You weren't within one mile per hour, because the truck might say its going 60 but is going 59 absolute speed (what the gps would read). So, if you were 1 mile per hour off w/265's by checking your actual speed compared to the "shown stock speed", which is actually 1 mile per hour off, you are 2 miles per hour off in total compared to stock.

In theory the 265 tire on the same rim and a 75% ratio will make the truck roll 3.88% faster at the same revolutions.

So, in theory if you're going 60mph (off gps) with the stock tires, and then go the same speed (when the needle on your speedometer is at the same...about 61) with the 265's, it should read about 62.3mph. Now, that's theory!;)

Of course in reality, factors such as tread depth and the likes will make the numbers a bit different.

Add about 5% to what your DIC reads.

Fact though is that the lb7's just get better mileage.

Hope this helps.

Later.

I can't get less than 18 MPG Combined city & highway! For the pas 2,000 or so miles I haven't reset my DIC and it's stuck on 18.0 MPG. How in the world can you get less than 14 mpg not towing? If I was getting 12 MPG my truck might have to burn;) I could see the clutch fan fully engaged if the engine was hot killing MPGs though.

There may be something to the clutch fan. I was having A/C problems and they replaced the clutch fan & a week later it was burned out again. Could that effect my mpg's that much? If so, that might explain my 12 mpg.

Thanks for any input.

today i got 13.6 hand calculated on my 05 and about dropped a duece 299.9 miles on the tank. That is the best I have got yet. My 03 gets 17.9-18.5, 375 miles on the tank consistantly which I am ok with based on how it is set up. I never even look at the dic to be honest I forgot it was on there. My 05 is almost identically set up with the exception of the truxedo, AFE versus K&N. The 05 is crew the 03 is ex cab, the weight and brand name of the intake should not make that big a difference. I have been very disappointed in my 05 but I will keep it. I hate the lag of the line however.

I've got 2500 miles on my 05. I put 345 miles on the last tank before I filled, and part of that (125) was on the freeway. Hand calculated out at 16.8 with 220 of that around town.:) Next week will be pulling the trailer, we'll see.:rolleyes:

Happy Trails!

My '04.5 got its best mileage when it was new (15 city/19 highway). Now at 22,000 miles, the mileage has steadily decreased to where I only get 13 city/15 highway. Bone stock truck except for 265/75/16 BFG AT KO's, 5 turns up on the bars, and Transynd in the Allison. Numbers are hand calculated with 3.9% added to miles to compensate for the larger tires. Truck runs just fine like it always has from day one. I just don't get it...

Some of the things that I have done to increase mileage is using 5W30 Mobil 1 oil (good for about 1 mpg), lowered the front end by removing the torsion bars screws, bought an air dam from the GMC dealer that I had to shorten and redrill holes to mount it. These changes have increased my mileage from 14.7 new to 18.4 (12,500 miles). This is running at 65 MPH lite.

I am now trying 2 ounces of pure acetone added to ten gallons of fuel. An article on the net indicated that a 20% increase is possible. I'm on the first tank, and it seems to be improving mileage. Do not use too much acetone as it can actually reduce mileage at about 5 ounces per 10 gallons. Do not spill it. It will remove paint. If this works, I should be getting over 20 MPG with a 2500 crewcab 4x4. The article indicated that the acetone has been tested on o-rings, seals, etc. with no bad effects (gasoline was worse).

Given that the fuel rails are at 23k psi. This makes things a bit different for our truck...

1. At high pressures (and the high temps that come along with them) - corrosion is accelerated.

2. The injectors require a much higher degree of lubricity in the fuel. 450 microns wear scar diameter on a HFRR test. If the acetone washes away the lubricity additives - which adhere to the metal and provide a boundary layer... Well, I think you get the picture....

jeff

I added an intimidator to mine which will program the factory speedometer for larger tires and different rear gears. Im guessing by doing this my DIC is reading correctly. I stacked this intimidator with the edge, NOT for power but for the specific fuel delivery for good economy,,,,, bottom end torque, and fuel advance. The intimidator comes in as soon as the throttle is touched, the edge comes on as boost is indicated. I now average 22.5 in town and 27-32mpg on the freeway from 60-75 mph. :ro)
While cruising at about 68 mph, the edge inticates throttle being at 26% while the engine load is at 23-24%. This lly would not run with this low of load and throttle opening withought the intimidator. Makes sense to me. My Kodiak 4500 weighing 17000lbs with edge on LB7 at #5 with most smoke averages 42% load at 65mph,, and I get 13mpg with this truck. I will soon be checking my DIC by the numbers and let yall know.

04.5 GMC 2500 Crew,Short,4x4.
ATS exhaust,no cat,ATS full intake,egr blocker,fingerstick,edge,juice,intimidator.

Count me in with the bad mileage bunch. With the edge on 3,and boost on two I get about 13.7 mostly highway miles. I used to get 17 driving the same way with my 02. I will look into a dealer reflash as well. This is bull****. BTW I always hand calculate. I admit I am in the gas a little more than most so I don't expect the best mileage,but this is rediculous.:help:

I just got into Amarillo, calculated by hand and the DIC,(they were very close to one another). Ran cruise control most of the way 385 miles and got 20.3 at 70 mph. Best I have done so far, worst has been about 16.5 running between 73 and 85 through the mountains.

You will not believe this. I do not believe this. I have a 2004 LLY, 1 year old, 35.4K miles. I just recorded 24.75 mpg, average DIC, pure highway driving. Today.

Drove 80 miles on a two lane road to visit my mother. Typical rural road, winding through small towns with one big down stretch while approaching the Mississippi River (becomes a big up on the way back). I have driven this road a hundred times. I reset the DIC as I leave town. I set the cruise control on 63 mph. I take a final reading as I enter the town where she lives. No A/C. No wind. Today's reading 25.0 mpg. I am not making this up.

I noticed a surge in the engine at idle when I got off the highway, so I took the truck in to the Chevy dealer in her town for diagnosis to make sure there was nothing that was going to stop me on the road on the way back. I could not give them enough time to get to the bottom of the problem, and this is what the technician wrote:

"Checked for codes and there were no codes present. Verified the surge. Checked for updates and PI's. Found a PI that suggested to check for updates. Found an update. Installed the update and the same condition was present. Monitored the data and found the balance rates fluctuating excessively and the fuel pressure also fluctuating excessively. There was a PI that stated that if the balance rates were -4.0mm and 4.0mm in park to let the vehicle go at this time. The balance rates were within. Customer had to go at this time. Could not further pursue the condition."

The technician's next step was going to be to call the factory. I have no idea what some of this stuff means. Don't know what an SI is. Don't know what balance rates are. I am doing searches on the Diesel Place to try to get some answers. Well, saw this thread about fuel economy and thought I would tell you what I am experiencing.

At any rate, on the return trip, I reset the DIC at my normal starting point. No A/C running. No wind. Until I got to the Mississippi and started a long uphill pull, I was at 25.6 mpg. This is the highest fuel economy I have ever recorded on this vehicle under any running condition. They must have changed something at the dealership when they did the "update", that's all I can figure.

My final DIC fuel economy on the return trip was 24.5. Average of the two readings was 24.75 mpg. I can not believe this, but I ain't complaining. This truck has always gotten great fuel economy.

So that is my story on fuel economy.

I am concerned about the idle surging. I looked at the stuff on this board and found the word "reluctor". If it is a reluctor problem, this is a serious thing as it can stop me dead in my tracks. Could my problem be the reluctor when the fuel pressure is fluctuating, along with the "balance rates" fluctuating (whatever the balance rates are), or do I likely have something different going on?

Any

You guys might be better off to hand calculate and forget your DIC! Sorry about the pun! Any mods at all seem to throw my DIC's off a ton.

My truck is 100% stock, no mods. I checked the DIC early on and it was off by 2.5% from hand calculated mpg - 1/2 mpg off at 20 mpg - so I have always trusted the DIC. My truck is 2WD, which helps. Allison tranny, which I forgot to mention before.

My mileage has always been excellent. I picked the truck up in Texas, new, and drove it to Minnesota. In the first 100-200 miles of the trip the DIC was reading about 17 mpg. Then it gradually started to climb. By the time I got home, the DIC had read 20 mpg for the last 200 miles of the trip. This was all freeway driving on I35 at 65-70 mph. I now drive routinely cross-country at 70-75 mph, sometimes 80 mph, hot/cold, AC/no AC, with the wind, against the wind. The worst I can ever remember logging on the DIC for a long trip at freeway speeds was about 19. The best was about 22. At lower speeds, the mileage has been spectacular.

My truck is 2WD, which helps. Allison tranny, which I forgot to mention before.

My mileage has always been excellent. I picked the truck up in Texas, new, and drove it to Minnesota.

Off Topic... BillK, why a 2wd in Minnesota, or are you from TX??? Just wondering.

I really can't complain about my mileage either. Even since putting 265 BFG KO's on mine, I've been seeing about 17.5mpg (yes, adjusted) on every tank. That's @ 70-80mph on highway with some intermittent city driving. I was getting 16-18mpg before the bigger tires... so about the same.

There are so many variables that affect fuel economy that it's very hard to tell anything for sure... I found out today that my #2 injector was failing and the dealer replaced it. Now having that fixed should in theory help my mileage #'s, NO? I guess time will tell.

mnoutlaw, you'll probably need to give your truck more time to break in before you can tell for sure where the mileage will be. Mine was all over the place for the first few thousand miles. My first tank was over 18, then I didn't see over 16 for about the next 3,000 miles. Weird, huh.

-AJ

It's a funny story. We had a '98 FWD Tahoe on lease. We used the FWD twice in three years, and one of the times was just to try it out. We started spending more winter time in AZ. We bought an '01 Yukon. I decided on 2WD (bought in AZ) with traction control and positraction with low numeric-ratio rear end (3.42?) for lower initial cost and operating economy. Worked great. Come time for this pickup, the MN dealer could get 2WD truck but would not give me anything for my 2WD trade - got a lowball deal, $5K less than book. I knew a used car dealer here. Asked him what is the best market in the USA for used 2WD Yukons. He got on his computer and looked at the lastest Manheim Auction records. Told me Dallas-Ft. Worth. I called two Chevy dealers down there and both gave me over-the-phone trade in offers of $17K on my Yukon, as opposed to the $12K my local dealer would allow - same exact $$ for new truck. I got in my Yukon and drove to Big D.

Truck has positraction and 2WD, and I love it - cost less to buy and less to run and less things to break and go wrong (although I never had a problem w/my '98 4WD). For the times I am in MN in winter, I throw 500# of water softner salt in the box and have no trouble at all, and I don't think I would really need that.

MN is 4WD country - period. Start driving South on I35 and get to Kansas City, and it is still 4WD, but when you say the word "Twowheeldrive", you begin to get a look of recognition. By the time you get to Okie City, they follow what you are saying and can give you some choices. Come Dallas, they will smile and talk to you and treat you like a normal human being if you have 2WD.

I agree with your comments about break-in and fuel economy. Mine got better right away, as I indicated earlier. But to get to best fuel economy it took many thousands of miles.

This is my first Diesel p.u. My truck is getting about 15 mpg w/ 50-50 street & highway driving.To me this is way better than my gasser Ford was getting & with way more power.The best I have been able to get is about 400 miles on a tank of fuel.My truck is an 05 2500hd crewcab 4x4 shortbed all stock.

It's a funny story. We had a '98 FWD Tahoe... MN is 4WD country - period. Start driving South on I35 and get to Kansas City, and it is still 4WD, but when you say the word "Twowheeldrive", you begin to get a look of recognition. By the time you get to Okie City, they follow what you are saying and can give you some choices. Come Dallas, they will smile and talk to you and treat you like a normal human being if you have 2WD.
Yeah, that's pretty typical I guess... I lived in E TX for 4 years and can see what you mean about there actually being a market for 2WD trucks. Much better there! I can understand your reasoning for having a 2WD, besides having 4WD up hear just means you can usually go a little further before getting stuck! :p:
Well, enough of my off-topic :blahblah:

-AJ

I don't know why I hear so mush complaining about mileeage. It's a truck not a yugo. Remember when trucks got 6 mpg at 55mph. Speed limits are faster than ever and I hear lots of winning about bad mileage. You can't expect the goose to lay a golden egg men. All these mileage reports hardly ever have all the facts. I personally wouldn't go by the DIC. What a name by the way. I would do it the way my grandfather showed me. It's been around for years. Do you want to know what it is? MATH!!! Fuel prices are high and it will get worse alot worse. It sucks but I love my truck and I will fill it up with a smile everytime because I am a truck man.

2005 2500HD Duramax Bone Stock and I like it that way for now.