We use to own a 2001 f350 powerstroke, it got 12, uphill, downhill, empty, or pulling 18,000 #'s, not sure how yours is, but ours never changed in the 70000 k's we had it. Our '03 Duramax pulled 22 - 25 empty, and 15-17 tugging. Our '11 so far is no where as good.