Something I have not seen mentioned is the cost of maintenance, I had a powerwagon with the 6.4 and now have a 2500 with the cummins, the maintenance costs of the diesel need to be worth it for how you are working it.
The mileage is better and I tow alot but if I had it to do over again I might just get a 6.4 for the reduced cost of maintenance over the long haul.
I mentioned this in another thread (I did the math in a spreadsheet over the long haul before ever buying one), but the cost of maintenance on the Cummins isn't really much different over the long haul than the gas burner equivalent. I don't let that factor into my decision as to whether or not I go diesel over gas. After owning 2, I can say for certain in my case that my math worked out.
Oil changes cost more but are half as frequent. My 16 3500 cost me $94.50 changed at 15k miles. My 18 Hemi cost me $58.40 changed at 5k miles. So it cost me an additional $80.70 to go 15k miles.
Fuel filters are about $100 every other oil change. But diesels have no coil packs or spark plugs.
Trans fluid changes are roughly the same cost. The 68RFE intervals are 60k severe duty or 120k miles normal duty. The 8 speeds are 60k miles.
The Cummins doesn't suffer from potential lifter/cam issues nor header bolt issues.
The only real cost adder is the DEF system, but you have to pay to play on that one. Delete it or fix it and roll on. I think you'd be hard pressed to find nearly as many Hemis on the road at 400k+ miles as a Cummins (still on stock everything in the engine) so if longevity is a real concern it makes a lot of sense to go with the Cummins.