My 08 6.4 crew cab short bed dually fx4 with 4.10's is averaging 11.2 so far. But it does only have 1300 miles on it. I am hoping this will improve with time. My 85 6.9 crew cab long box with 4.10's and a zf 5spd would average 15 empty and 9 pulling 15,000 at 65.