:confused: MPG'S SUCK!!!!!!!!!!! Just returned from a 4600 mile trip from Michigan to Glacier National park and Cody Wy. This was my first long trip with a diesel pulling my 11,000lb 5th wheel camper. (mpg's not any better then my 99 6.0 chevy 2500hd gasser.) Only got a average of 8.0 worst was 7.5 best was 8.8. Short trips before that I got 9.5 to 10.0 these are all hand calulations. Truck is a 03 D/A with bfg 285/75r16 tires it also has a Bullydog power pup installed set on the 40hp gain and I have recallibrated for tire size. No other mods. It didn't seem to make and difference how fast I drove.which was normaly about 68mph watched rpm"s 1900 or 2200 didn"t matter either. A/C on or off no differance. Air filter is clean (oem filter). change fuel filter at camp ground thought that may help, had 9000 miles on that filter.No change in milage. Took power pup off no change just lost a little power. Truck doesn't seem to have any more power then my 99 gas truck. This is not the mpg's I was hoping for. Do I have a problem with the trucks Injecters? HELP

Thats what it sounds like to me. My milage started dropping and then I noticed white and black smoke. I had my injectors replaced at 26,000 miles and I now have a little over 27,000 miles. After the injector replacement, my milage is back up to around 17mph with all of the add on's that I have listed below.

Putting on taller tires has raised your gear ratio which makes the engine work harder. The stock tires were 245/75-16 which were 30.5 inches in diameter and the 285's are 32.8 inches. 4.10 gears rather that the 3.73's that you now have would drop the RPM's back to stock range and help on the milage. If you are comparing your stock milage to what you have now the tires do affect it.
Have a nice day.

looking at my mpg's 7.5-8.0, seems that others are getting 11.0-13.0 with 285

285-75-16 tires will not even phase the duramax--mpg's should stay around the same as 245-75-16's, maybe drop a little bit. Sounds like your injectors are going south to me

On Flat land (S Florida) I average 10.5 to 11.0 mpg pulling my 11,500lb 5er toy hauler. I have 265 tires and do not tow over 65mph.

Bob

So, should I contact the dealer and have them look into the injectors?

Do you have any of the other signs/symptoms? If all you are getting is lower mileage than you planned on, it probably is NOT injectors.

seems to have a lack of power, my 99 chevy 6.0 had as much power as the diesel has.

Do you have the shuttering, the smoking, or any of the other symptoms though? Loss of power, or less MPG thatn you expect alone does not mean bad injectors. The balance rates need to be checked, for one.

no just seems to be a loss of power and bad mpg's does not smoke, oil level is not to high. but on the other hand from what I have read on this forum this seems like very low milage for this truck or everyone else just lies about milage.

There are lots of factors, such as terrain, wind, any number of things. People jump to injectors when it may be the simple fact you were driving into the wind, or got a few batches of winter fuel left over.

I know, I have thought of all of that, one or two tanks of fuel I could see, but after 4600 miles and never any better then about 8.8 with the wind if I remember right. May I just had bad fuel and drove into the wind for 4600 miles. But then everyone else I seem to talk to lies about MPG'S with the Duramax.

The dmax should beat the 6.0 handily MPG-wise. While camping I talked to a gent who pulls a 35ft 5'ver. He traded his 2000 6.0 4.10 gear truck in for an 05 duramax. Towing MPG (same trailer) went from 6MPG to 12MPG running 65MPH. He also said he has much more power than before. He IS running stock tires. ANY tire size increase WILL negatively affect your abilty to TOW due to the increase in gear ratio.

I pull a 26FT TT with my 03. My towing MPG is 11-12 no matter what speed, load, etc. My best MPG seems to be around 65-68MPH, the engine seems much "happier" in this range, running 8-10PSI of boost versus 4-6PSI when running 55-60. I have noticed a MPG difference after filling up which I attribute to a higher or lower cetane rating. Yes I run an additive in every tank.

ok,Fred thanks my 99 6.0 has a 4.10 rear end also. do you have stock tires on your truck?

I only get 8 MPG towing my 5er as well (36' in the neighborhood of 14K up and down hills on the way to the beach). I attribute that to the fact I am running 295/75/16 tires. I know that when I am in tow/haul mode my truck wont shift into 5th gear even on flat land. I have since put a Predator on and am seriously considering a gear change to 4.10's.

I thouhgt D/A only came with 3.73 rear ends.

It IS most likey your tires causing the poor performance. I have 265's and get a constant 9-10mpg towing what's in my signiture, and it weighs 18K pounds. When I had my 35' Keystone Challenger which weighed 14,400lbs and 265's I would average 10-13mpg, until I put 285's on it. Mileage went down into the 8-9mpg range and was a gutless pig pulling the 5er. I took the brand new BFG AT/TA/KO's off that I had just spent $1000 for and bought 265's again. Problem solved, back to the same power and mileage as before. Take it from someone who has had both, and pulls alot, get smaller tires. I bet the bullydog isn't helping one bit either fuel mileage wise.

I can't see going to 4:10 gears on the D/A. This motor has so much power under stock configuration. I recently drove from Alaska to California and it was nothing but Mountains all the way. My picture shows my truck with bed camper and a 20 foot trailer. My total weight was over 23,000 pounds and I had no problems maintaining 65 mph going uphill. I personally would not increase my gears and lose mpg when not needed. I have heard that GM put the 3:73's in as standard equipment but they do offer the 4:10's as optional. I have stock size tires and with my truck fully loaded, I got 10 - 10.5 mpg the entire trip. On an empty load I average 16 - 19.5 mpg depending if I am "playing" with my accelerator. :)

Jeff

Man putting 4.10 in a dmax and your probuley going to red line the tach at 65 mph. Plus I pretty sure that the 4.10 are not an option with the dmax/alley combo.

I personally have not checked, but a friend of mine over in W. Virginia called me 2 weeks ago asking what gears I had in my truck. He said the 3:73 came stock but they did have the 4:10 option. That may have been just that stealers salesman talking a line of @rap...

Jeff

You are right neverenuf the bullydog makes no diff. at all

I had 305 and am now running 285 and get 15-18 mpg with both tires.

hand calculated or DIC?

When I bought my d/a dually used it had 255/70x22.5 on alcoa's. I went from Ocala FL. to Ma. on 2 tanks of full I figured 18 mpg. When I tow my horse trailer[5th wheel about 10k] in the hills of New England I get around 12 mpg's I make speed going up hills,I pass gassers w/ smaller trailers like they have stopped. No modes, just the tires and rims. I do my cal. using a gps. I have to use the gps because the milage is so far off 60 on the speedo is actually 73 over the ground speed.I'll tell you all black extra cab westin step up rails and the tires and rims look awesome

Came back from our Alaska trip about a month ago. We towed a 10k 5th wheel for 11370 miles round trip over some of the worst roads you could imagine. Averaged 11.29 mpg for the entire trip - hand calculated. We are running the Edge Juice on level 2, and have 265/75x16 tires. Always had much more power than needed.
Stubby

The last big trip I took with my 5th wheel I averaged 14.5(hand) with 285's and the edge on 2. My camper is 28ft and is 10,800lbs.