I just bought a f350 cc,srw,4x4,6.0 I average around 16 to 17 miles per gl. I drive 42 miles one way to work twice a week all highway (other 2 days I carpool). I usally go around 70 to 75 mph at about 2,000 rpms give or take. All I know is it gets better milage then my old 2000 GMC 1500 with a 5.3.