LLY bad mileage when towing

[stockho]

I have a bone stock 04 4x4 LLY 2500hd with 6400 miles that gets great mileage when unloaded but miserable mileage when loaded.I only tow an 8k pound trailer and get 7 mpg in the flats at 70 mph.Im a tech at a chevy dealership and have checked all the usual stuff, but i was expecting much better mileage.All i hear from most dura-max owners is how great the mileage is.Love the truck but i'm disgusted by the towing mileage..

[gandrimp]

Yeah Ive got an 2005 LLY that only gets about 14 driven at 60mph.The thing only has 1200 miles but my 454 would get that.But it does run goooood.Been startin at 10 degrees like it was runnin already.My dads 2004 is gettin 17 to 18 driven about the same way.His is not the LLY.

[More Power]

Are you guys running stock rubber? If not, have you corrected the speedo?

MP

[stockho]

I recently changed tire sizes up a little but the effect on mileage was minimal.It went from 8mpg to 7 mpg..It was terriable with the 245/75/r16's factory tires.If i re-program the tire size, GM will not warranty the transmission..The allisons that are coming into my dealership blown up, are the ones that are preprogrammed..

[lburks]

Towing a 13K 5th wheel I get an average of 10mpg. Mileage goes down when out of Calif. because I drive 70.

Around town and commuting its 14.5 average.

When running empty I have not gotten more than 19.

What do I do to get the 20-22 that some get?? Get out and help by pushing???

[HalsMax]

I tow my racecar/trailer to the track often. Weighs about 5500# give or take. I always get 16-17 MPG while on the highway pulling this load. Unloaded highway I get 19-20. In town to work and such she gets 17. My truck has about 6K miles on her and has never gotten worse than 15 on any tank of fuel. Mods are a Hypertech tuner (stg 1 or 2), K&N filter and Flowmaster muffler. I run Rotella Synthetic oil if that helps any.

[MPH]

I have about 2000 miles so far on my 05 LLy, and all i can say is i miss my 04 LB7! I am seeing 14 empty, and pulling a little two place snow machine trailer with two sleds, i'm seeing about 9 mpg. so far i am very dissapointed!

[gandrimp]

Mine has stock rubber and no performance ups.

[Heartbeat Hauler]

Stockho,
You know, you only have 6400 miles on the thing so it may get better after breaking in a bit. However, I would agree that 7 mpg is awful seeing how my 3500 4x4 gets about 13 mpg when towing my 9500lb 5ver, and that's at about 70 mph and I get 16 mpg around town (empty). The other thing is have you changed your air intake, i.e. an aftermarket air filter, etc.? If you have there may be excess oil on the MAF sensor. If you find out anything let us know.
JP
P.S. I kow you have fears about reprogramming for the tire change, but I would do it. It eliminates one variable.

[stockho]

thanks for the input on the LLY's with bad mileage.I haven't done an intake or air cleaner yet so the MAF oil isn't there.It's totally stock except for slighly bigger tires.I could reprogram the computer i guess and see if it helps.It seems like the addition of the EGR ruined these engines.Anyone else have an LLY drinking gas?

[rickdlance]

I have tried a air intake, a 4" exhaust, egr, blockoff plate, Edge Juice, Quadzilla, Predator, and "cat-less", and so far I am 10 to 20% below the 3 LB7's I have owned on mileage. The LLY also does not pull heavy as good.

[stockho]

rickdlance..how many miles do you have on your lly's..did the gas mileage improve with more miles? Did the juice help? Do you like the banks system?