New tow vehicle...6.4 hemi or Diesel?

6.4 hemi is a 4.10 gear, no thanks with the 8mpg towing maybe 15 on the freeway
I have an 06 2500 5.9 Cummins it gets 16mpg loaded & 20 mpg at 70 mph.
plus the safety of the engine brake and Tow/haul