6.4cor 6.7?

My Host Mammoth is 4712 lbs dry. By the time you add 60 gallons of water, occupants and personal gear, you're pushing 6000 lbs. The 3500 will be able to carry it, but don't plan on towing anything with tongue weight at the same time using that truck.

The 6.4 Hemi will do fine just carrying around the high profile camper even if it does sing pulling grades. If you plan to tow behind this combination, you need to look at the 6.7 CTD. Although the gasser is lighter than the diesel, all the weight is up front. In real world use, that rear axle will be loaded about the same regardless of your engine choice.

For just the TC I think the gas engine makes the most sense; it's less expensive and gives you more payload.
If you intend to also tow a trailer of any size then the diesel might be a good idea.

If you're towing or carrying heavy on a regular basis there is no substitute for diesel power. Especially if there are any steep grades to climb.

Both great trucks. If you get a gasser, get the 3.73 gears at a minimum, if not the 4.10's. The big Hemi creates a LOT of HP and torque, and you can buy a LOT of gas for the price difference of the Cummins (if you don't need to power from the Cummins).