I have a 2002 with a stock duramax. I have two friends whose trucks have the same stock engines (a 2003 and a 2004 with the LB7) and they both get a consistant 23 mpg on the highway (hand calculated), I get 18mpg. This is measured on trips to Spokane over mountains with the cruise set at 75mph so there is little individual driver difference. I get about 350 miles to the tank, they get 400 and more.

So what gives? I have recently had the injectors changed and it looks like I lost 2 mpg on the highway after that. I also have the six speed transmission conversion so if anything I should get better mileage than they do. We all have 245 stock tires and 373 rear gears. All three trucks are extended cab, short box 4X4's. All peas in a pod as nearly as I can tell.

I cleaned my MAF sensor, changed the fuel filter and air cleaner, and made sure none of my brakes is dragging. Prior to changing the transmission valve body to a six speed I got 17 mpg at sustained 75 mph so at least the conversion help something.

So what gives? Any ideas?

get new friends :D

Has your truck ever achieved good mpg? It could be that new your truck was like that...not sure if you are the orig owner.

Injectors reman's from GM?


My LB7/04 is like your buddies...22-23mpg.

I thought the early trucks 01/02 did the very best in mpg.

Your buddies are messing with you man. If they are getting that mileage either they are driving the highway every day or reading the DIC.

I have a 2002 with a stock duramax. I have two friends whose trucks have the same stock engines (a 2003 and a 2004 with the LB7) and they both get a consistant 23 mpg on the highway (hand calculated), I get 18mpg. This is measured on trips to Spokane over mountains with the cruise set at 75mph so there is little individual driver difference. I get about 350 miles to the tank, they get 400 and more.

So what gives? I have recently had the injectors changed and it looks like I lost 2 mpg on the highway after that. I also have the six speed transmission conversion so if anything I should get better mileage than they do. We all have 245 stock tires and 373 rear gears. All three trucks are extended cab, short box 4X4's. All peas in a pod as nearly as I can tell.

I cleaned my MAF sensor, changed the fuel filter and air cleaner, and made sure none of my brakes is dragging. Prior to changing the transmission valve body to a six speed I got 17 mpg at sustained 75 mph so at least the conversion help something.

So what gives? Any ideas?

I can get 23 mpg with my 05 LLY, but only if I keep the speed under 70, At 75 I will drop a few mpg's. I'm running stock tires as well, but with an extended cab, long bed, 2wd...

I call BS. Sure there are some trucks that get good mileage but 23mpg at 75mph is stretching it. 23mpg at 55mph maybe.

tailwind doing over 75 I got 22mpg.

tailwind doing over 75 I got 22mpg.

Tailwind and/or downhill I would believe.

id be happy with 18 2002 slightly modded getting 15.4 hwy

Are you or your friends using any type of tuning? I got 23 mpg b4 lift on 285's with stock rims @ 70mph hand calc 2002 lb7. installed 4" lift with 35x12.50r20's got 16mpg avg. just went back to 285's and stock rims now im seeing 20ish.

Tuned i only got 15.5 ALL hwy at 70mph.

Getting 19 constantly at 75 and can get 21 if I keep it to 65 max. Took lots of tuning to get this even.

I got 22mpg with 265/75/16 on stock wheels doing 75mph, slight tail wind @ 10mph maybe. Same tires at 80mph 19mpg. Now with my new bfg a/t ko's 285/65/16(stock wheels) I'm down to 17mpg highway if i'm lucky......altho I might be getting winter diesel fuel now so a drop in mpg is expected...so I can't tell the truth til spring.

You could have a stuck open thermostat. A cool engine is a fuel sucking engine.

I just calculated my first tank that I ran through me new (to me) truck.. 14.5mpg :o:... Hopefully the "new truck" :driver: sydrome is wearing off and I'll be able to bring that number up!

I get 14 mpg mixed driving on hummer take offs. With a mild 35 hp tune. Mileage is definately mixed and varies between vehicles, even those with similiar motors/configuration.

No better than 16.8 I run on level 1 with the EDGE @ 70 mph on cruze

I Can Get 22 Running 72mph With Only Me In The Truck Or Should I Say Did Get When I Had 305 5020 Nittos On It. Now With Toyos 20 Is About It At 70. Tire Brand Can Have A Small Part Of It 2. Even Though They Are All 245's On Companies Tire Could Weight More Than The Other.

hey I have a 04 and at 65 on the stock 245s I could get 23 24 hand calculated I drive 100 mile round trip to work daily all highway. have two friends who have IDENTICAL trucks to mine crew cab shortbed 4wd. just a few months differnce. one babys his truck from day one. he gets 19 tops. the other normal driver 20. I ran it hard for the first ten thousand miles. and get great fuel milage after it broke in. above 65 my milage drops. I do have a ? since I read you changed the valvle body on your truck. were did you find out about it and were can I? here? I am new still looking around on the site.

suncoast sells the 5 to 6 speed kit, some performance companies carry them http://suncoastconverters.com/gmc/gm_products.html ...i get like 15-16mpg average, regardless of tuning everywhere from stock to 425 on PPE...and i figured it was so bad with PPE cranked cuz of the smoke but it didnt change, mine is mixed city highway...it could depend too where u guys are getting fuel tire? tire pressure? do u all have spares? tonneau covers?...and during plowing season i average like 11-12mpg if i'm lucky but that is alot of idling.

i can do well over 20 if im doing 65 or less. anything 75 or above and it goes through fuel.

thanks black demon. I found some info also. I do carry a spare and have a tonu cover and tool box. in the winter it changes when they cut the fuel. I run the (bad) diesel or the cheap hi sulfur fuel at the truck stops if I have the choice. I dont let the truck warm up I hop in and hit the road. I do baby the truck till it warms up and shifts to normal rpm. we run the same oil and had the same tire size. I have 285 on now and my milage corrected is still better. it was even with the 315s I ran for a year.

Mileage will vary from truck to truck. Sometimes tuning will help. When I bought my wifes 01, it only got 17, I installed a Hypertech and set it to 90 hp and the truck gets a constant 20 hiway. Around town is always less due to warmups and cold running engine. On my truck, I get best mileage at 65 or less with edge on 5 and ppe on 5, barely need to touch the go pedal to maintain speed. My mileage dropped a little with the addition of a flatbed due to loss of aerodynamics.

2004 California EGR NO cat Lb7: I get 18.5 to 19 mpg running 75MPH - if I slow down I can get 20-21 around 65mph with 265/75/16 Michelle LTX Front at 72psi rear 65psi. I usually average about 18-19. All stock crew 4x4 120k miles. (My D.I.C. says I get 20-22.5 and has never been correct.)

Hoping to do a little better since I just installed a 3rd set of injectors this month. It sure runs better and smokes WAY less....just like new. Takes the pain of injectors issues away..a little.

Switch trucks with one of them and see for yourself.
I could get 21-22 out of my '02, but not anywhere near 75mph. Only at 60mph on state roads in the flatlands. Mine would avg 18-19mpg at 75 in the mtns. Less in winter.

You would be surprised how much you accelerate past 2000 rpms in traffic drastically affects your mpg....

Switch trucks with one of them and see for yourself.
I could get 21-22 out of my '02, but not anywhere near 75mph. Only at 60mph on state roads in the flatlands. Mine would avg 18-19mpg at 75 in the mtns. Less in winter.
Have you ever been on the same trip as they have? I had a friend that made a high mileage claim on his Dodge. Then we were traveling together on a 300 mile trip. When we got fuel he had a list of reasons why he did not do so good that day that was longer than my arm.

I call BS. Sure there are some trucks that get good mileage but 23mpg at 75mph is stretching it. 23mpg at 55mph maybe.

yea this!