Haha. I trust mine. I have a BS in engineering.

4. You need a new truck!

Feel free to come along on my next road trip and we will hand calc the mileage together.
35 gallon tank, and I have gone 700 miles on a tank without running out before..........you do the math.

Hey you must have the "good" one the factory made that year, maybe your 700 mile trip is all downhill, maybe you were the secret test boat driver for Fountain and know all the secrets to getting the best performance out of everything you run! You just seem to get numbers nobody else can. I had a non-DFP 2wd duramax crew that saw 17 as a high (brand new, unloaded driving 200 miles home from the dealership). The rest of its life it got low teens and the truck was bone stock for the whole 175K miles I had it. As a friend of mine from Ireland says, hey that truck is big and heavy and it is punching a big hole in the wind so don't expect any great performance!

http://www.trucktrend.com/gmc/sierra-hd/

Oh, and the fuel economy, which we recorded as a combination of driving while towing and with the truck unloaded, was 13.6 mpg. :eek:

if you got 23-24 then you would get 828-864 out of the 36 gallon tank.......you would definitely qualify for the Guinness book! :D

Your numbers seem good but not record worthy! :D

08 Chevrolet crew cab Dually , EFI live, straight exhaust, lift pump, on economy sport tune 18mpg at 65mph average, 12 to 13 towing 14,000 lbs. winter months driving local and highway average 14.1 unloaded truck weighs 7800 lbs
2012 Chevrolet crew cab Dually not touched yet, averaging around 14.0 around the city, one small road trip I averaged about 17.5 very happy with that , I had some 6.0 liter fords prior , that were lighter and didn't get quite the economy as the duramax, also would not start unless they were plugged in over night in the winter months ,
I have also found if you barely touch the gas pedal and play the MPG game I have scene 20 , but that's aggravating and no fun, put your foot into it fuel is cheap for now

I guess I just got a good one.......we'll leave it at that. Maybe the elevation has something to do with it I don't know. 5,500' here.........thinner air= less resistance? Also = less power.
As far as getting 850miles out of a tank? I don't drive 65

The fact that my front brake pads have 163k on them and still have about 1/3rd left on them should tell you something as well. I don't thrash my truck or keep the gas pedal on the floor constantly. Maybe H&S tuning just has an awesome program? with 150 HP Hot setting, I can floor it.... and hardly any visible smoke from the tailpipe. You probably don't believe that either though lol.

Wow !

Did they forget to put pedals in your truck ? LOL.

Amazing !

The Diesel Power Challenege is always done in Denver, the trucks hate it. Huge power loss, run like crap compared to where they come from. You must drive down hill every where you go.