I am not sure if I believe some of these mileage claims but once you go Cummins you will not regret it. My 06 gets and average of 16.5 making a tick over 500hp at the rears and will still get about 12-13 towing 10k.

Josh

70 Challenger
1960 Town Wagon P Pump 24v cummins project
06 Mega 3500 Drw 2wd
12 Durango R/T
18 Power Wagon
67 A100