Cannot comment on the the 6.4 but would think it would be better then my 5.7 that used to haul my 8000pd camper. The 5.7 never felt lacking in power even up long inclines of 1000 feet in elevation it did the job well, milage regardless what I did was giving me the 8.9mpg towing area. Only thing that changed fuel milage was a good tail wind. Again the 6.4 being a bigger engin would have more pull, plus am told they run on 87 octane not 89 and would save a little at the pump.