Gas tow vehicle for fifthwheel

Hedgehog, You've made it clear a diesel is not on your choice list. Others have suggested the 6.4 Ram simply because it will do the job you require as well or better than the others. 14000 miles empty with the cylinder deactivation would return some honest fuel savings. But, between the 2, as much as I like the new GM's, that 6.0 is not as strong as I would like pulling 12K or more. Those hills will seem mighty long. I'd head to the Ford dealer and order that F350, 6.2/430:1 in the exact color and configuration desired.
It may burn 2 or 3 gallons more each week, but will pull the load fine.