Allan, you seems to be a smart kid!
But you are kinda abscess, with that MPG
I guess, we already determined, that driver plays the huge role in that, and that's the only constant here.
The rest will depend on way to many things, to specs a truck solely on a fuel economy....
Besides different engines, perform differently, at the same RPM.
IMHO 1) Truck should be able to do the job, and make the driver comfortable, while doing it!(Didn't mean sleeper)
And 2) Be as efficient as possible, w/o sacrafising #1! :wink: