Originally Posted by Blacklung
Just about every new diesel owner refuses to believe that their truck doesn't get 25 mpg. The best I've seen out of my 5.9 on 35"s was about 19 MPG taking it incredibly easy on the highway with my Comp box on 1 and the fueling turned all of the way down. A while back, some guy on cummins forum was trying to convince people his truck got 26 mpg. When he got called out, he came back and claimed he got 22 mpg "hand calculated" and was all upset that his mileage was so poor. I just laughed.
In all honesty, the best mileage I've ever seen came from my dad's old '02 Duramax. That truck could get around 20 mpg on the highway on stock tires. Now my '99 7.3 rolling on 44"s... I don't even want to talk about that.
My 02 duramax with PPE hot ET I got 20MPG as well. Granted that was with a sled in the bed, and 60mph easy driving. Same conditions this year I got 19mpg with my 6.4L with a sled in the bed and a spartan 250 tune (60-65mph).