other than the 1-2 gearing gap, everything I've read on the 6.4 ram with the 4:10 and even 3:73's seems to be very good as a towing platform if you choose to go gas.
Do yourself a favor and at least try the F250-350srw with the 6.2, with both 4:30's and 3:73's they are quite the beast with a very well geared and proven transmission behind it.
Regardless of what you do both the Ram and the Ford has very potent gas V8 options. The Gm option is a good truck however I think they have a little work to do on their gas offering to get back to being competitive.