If I reset the factory meter, I show about 18.5MPG at 80MPH on flat (Texas) terrain. That's with a 4x2, 5.4L, 6.5' supercrew, 3.73LS rear, with a commercial ARE DCU aluminum topper (~350lbs) and a Ranch Hand full front-end replacement (~150lbs). I'm turning slightly over 2500RPM.