I have a GMC 2001 2500 Ext Cab longbed, 3/73's, I primarily use it for towing. I have 265x75 Bridgestone TA's. I did all the easy mods. Hypertech, 180 thermostat, Iridium plugs gapped at 045 from the factory. NAPA Blue Max wires, NAPA air filter, Magnaflow 50 series replacement muffler, Monroe shocks. I just completed a 600 mile trip towing a 10000 lb fifth wheel that is fairly aerodynamic.. A quarter of the trip was in mountanous terrain where you are pulling and decending 7.5 and 6.5 grades, love that allison in the mountains. Another quarter of the trip was city driving, too much stop and go, and one half was cruising the interstate 60-65 with the RPM's mostly below 2000. I got an average of 8. I think that is fairly good considering all the different types of driving.

Anyway, I just bought a stock 2005 2500 GMC Crew Cab, shortbed, Duramax. Will take me about a month to set up to tow, which will be in time for my next long trip.... Was just too good of a deal to pass up. I'll let you know how they compare. You know my fondest memories as a kid was the camper on top my dad's 1964 GMC pick-up. We've come along way...

I think you will be impressed with the Duramax for sure and should see a little better fuel mileage too.

I think you will be impressed with the Duramax for sure and should see a little better fuel mileage too.

Ditto,I just hope your 05 DMax doesnt run hot in the mountains,some LLY's will run pretty hot,and if that cooling fan is running a lot,dont expect great mpg until it disengages,and cools back down.

My last GM truck was an '02 just like your '01 without most of the mods. In comparing it to my Dmax the diesel gets 1-1/2 times the milage under the same conditions - be it running empty, loaded or towing.

I have a GMC 2001 2500 Ext Cab longbed, 3/73's, I primarily use it for towing. I have 265x75 Bridgestone TA's. I did all the easy mods. Hypertech, 180 thermostat, Iridium plugs gapped at 045 from the factory. NAPA Blue Max wires, NAPA air filter, Magnaflow 50 series replacement muffler, Monroe shocks. I just completed a 600 mile trip towing a 10000 lb fifth wheel that is fairly aerodynamic.. A quarter of the trip was in mountanous terrain where you are pulling and decending 7.5 and 6.5 grades, love that allison in the mountains. Another quarter of the trip was city driving, too much stop and go, and one half was cruising the interstate 60-65 with the RPM's mostly below 2000. I got an average of 8. I think that is fairly good considering all the different types of driving.

Anyway, I just bought a stock 2005 2500 GMC Crew Cab, shortbed, Duramax. Will take me about a month to set up to tow, which will be in time for my next long trip.... Was just too good of a deal to pass up. I'll let you know how they compare. You know my fondest memories as a kid was the camper on top my dad's 1964 GMC pick-up. We've come along way...Expect ~12 MPG with the diesel, maybe 13~14 on occasion if you keep the speed down.

I had an 01 8.1 traded for the Dmax. wish I had it back.

They didn't call it 8.1 for nothing :). 8.1mpg seems to be the norm.

Actually I've averaged around 9 towing my 10000lb 5ver, 10-11 city and 13-15 hwy.

WOW, my brother in law has an Avalanche with the 8.1. It has a AFE intake, TB spacer, and a Superchips tuner. It has 4.10's, and 265/75-16 it gets 12-12.5 every where. City, highway, loaded unloaded. Guess he's doing pretty good with it

Has anybody added Acetone to there gas for higher milage?

Has anybody added Acetone to there gas for higher milage?

I sure have,it doesnt do much for trucks with port fuel injection,but it helps the older TBI trucks,and carbed trucks even more.Typical gains for a TBI truck are 40-80 miles more per tankfull of fuel.Port fuel trucks may see 1/2 that if they are lucky.Carbed trucks could get 50-100 miles more per tank full depending on the truck,and how big the tank is.

I have been adding it for over 2 yrs now in all my mowers,and golf carts.I add it right to my 1000 gallon bulk tank,it improves fuel economy about 20-30% in both my carburated mowers,and golf carts.I run 25oz of acetone per 100 gallons of fuel.

Expect ~12 MPG with the diesel, maybe 13~14 on occasion if you keep the speed down.
Our Dmax doesn't get a whole better than our 8.1...I'm gonna guess 3mpg better across the board?

We have an 8.1 burban at the farm and it averages 10 with two horses in tow. Loads of power. My d-max only gets 4mpg better with the same trailer and same horses. Lots more power though.

Thanks for all the replies. My 8.1 has got as good as 15.5 on the interstate empty. It has been a good truck. Looking forwad to the D-Max. My first diesel.