mine is all stock. i have a mid profile 5th wheel thats between 9 and 10k loaded. i get between 7 and 8 mph with that. last winter, when the truck was new, we made a trip to the big horns late in the season with a 4 place open trailer. we drove 80 mph on the interstate and 70 on the highways. i averaged 9.5......i was not too impressed! empty i get 13-14.
my buddy with a 6.7 powestroke will consistantly get 2-3 mpg better than me doing the same thing (pulling, empty, etc...)
my buddy with a 6.7 powestroke will consistantly get 2-3 mpg better than me doing the same thing (pulling, empty, etc...)