The way you drive has a lot to do with the mileage that you get. You have to find the sweet spot for your combination and try to keep it around that spot. I know I have a chevy, but it doesn't matter, each combination will be different, mine is at 2000rpm, which is around 65, 66 mph. So I keep my speed under 68 and let the truck pull down on the grades, and not kick it out of overdrive until either it starts lugging or the egt, s start climbing too high. I run between 9.5 and 11 mpg depending on head winds and size of the hills.
03 Silverado cclb 3500 drw, D/A, Reese 22k hitch
07 Alfa SeeYa Gold 30RL,2 slides,power everything