I bought my 3500 srw in june hoping to get 15 or 16 mpg pretty consistantly. The best I have ever gotten out of this truck was on a 250 mile hiway run running between 60 and 70 mph and I got about 14.2 hand figured(no dic). Has anybody out there run in to fuel mileage problems with straight pipes on the lly? I got 12.5 on last fill up running empty mixed driving. Just rolled over 7000 miles.

My 05 3500 SRW 4X4 CC LB only gets 13.5 mpg most of the time. Adding 4" exhaust has not helped. Very disappointed in fuel mileage and power of the LLY.

I sure wish I knew what the difference was between your trucks and mine...:confused: My mileage has been anywhere from 17-20 since new...The only time I got 12-14 was on a trip with a tractor and trailer...going 85mph......I just have to wonder if this is a programming issue or what, since there seems to be a large mileage discrepancy with all of the lly trucks out there.

I am just about ready to trade it off but I don't know what i would buy unless I went back to an lb7

Is your's a 2500 or 3500

Rednek, what else do you have on your truck? I see in your sig you have 33's?

Road Boss, I have the edge w/***, and a K&N air filter. The 33's are only about a half inch taller than the 265's that came on the truck.

2500 rednek - still doesn't make a lot of sense to me....

Im running edge/attitude, full mbrp no cat or muffler and im getting anywhere from 17-21 mpg.....70 mph 2100 rpm...stocks 245's....also use stanadyne power in every tank as well.

I was getting around 17-19 mpg until it started getting alil colder and it has dropped to 16-17 mpg because of me letting it warm up longer in the morning.

Wow just browsing and Say this thread on fuel mileage again. There must be definatly be a problem with my HD because Best for fuel as an average on the DIC is 13.6 Around town and on the Freeway.
My Truck is a HD LLY DA Extended Cab 3500 Dually. Does that make that much of a difference?
Again thanks in advance advice and Great Forum!

Hey, Rednek, how many miles? These D/A's get better mpg with higher mileage. My "old" '01 got around 15-16 Hwy when new, then with 60k I was getting 18-19.
My new '05 only got 15.7 on it's maiden voyage of around 300 miles. Not to worry, it'll get better.

I was between 15k and 20k before I saw better mileage numbers.
I wouldn't throw the baby out just yet.She's not even broke in yet!
Blake

Mine is a stock 3500 DRW crew cab long box, just over 6K miles. I've been getting 14.2 overall until the last fillup, reset milage, now it's about 15.6 on open road. Usually cruise 75-80. After long trip, driving around town for the 2nd half of the tank, milage has come down to 15.1.

Im running banks full exhaust with no cat,banks filter, Also a 8 inch lift with 37 inch tires and im getting 14.2 in town and thats hand figuired,no tuner or programer yet.Stanadye in every tank.Truck has 5430 miles.

Im new to this forum and I have been reading these posts on bad fuel mileage. I have a 2004.5 CC 2500 HD with 20 x 10 inch wheels and 305 Goodyears, on the highway running 70 I am getin between 19.5 and 20.0 MPG hand calculated. I bought my truck in august so Im sure it was one of the last ones built before they switched over to the 2005's. 7500 miles on truck. Could when it was built have something to do with it? Computer upgrade?

What's your axle ratios, cause that'll make a difference too.:eek:

well at 7200 miles I thought it would start getting better, that's what I get for thinking):h . It is has 3.73 gears and I have already done computer upgrade to it once. I really like the truck so I would like to figure something out.

3:73 I believe is the only rear end that is offered for the duramax????

As far as I know all you can get is 3.73's.

I was thinking on the 3500s you could now get 4:10s but not for sure. My mileage has dropped with the cold temps and letting it sit for 20 minutes at a time warming up. With that said im getting an average of about 14.2 per DIC which seems to be pretty darn close to hand calculated. This is mostly back and forth to town with some highway but not a big highway trip.

On gmc.com they have 4:10 axles as standard on 05 3500's.

On gmc.com they have 4:10 axles as standard on 05 3500's.


And the 6.0 gasser as the standard motor....

My 04.5 lly 2500 gets 20.5 on the DIC and hand calculated on the interstate everytime and Im from PA in the mountains. I have 4" dual exhausts the rest is bone stock.