2009 6.7 litre with 6 speed auto 12 towing car trailer , will do 22 on the highway at 65. Had a 5.9 12 valve with a manual was a little better but not all that much. I have had 7 diesel pickups going all the way back to the first cummins in a pickup ( that was a gutless wonder) and none of them ever managed to get the mileage I heard claimed by others. On the flip side I did own a hemi ram and that was a pretty thirsty vehicle especially towing made the diesel seem like an economy car.