Gm just decided not to participate in the advertising for the highest tow rating wars. It means little. IIRC, when they all towed 23,000# up the Ike, the GM was fastest. I'll see if I can find the video and link it on edit.
Found itGM took 10 min 16 sec
Ram took 10 min 28 sec
Ford took 10 min 31 sec
to tow the 23,000# load up the grade.
To answer your original question, I'd say go for a 2500 if you choose RAM. Being that it will be empty most times according to you, the Ram 2500s rear coil springs ride way better than the leafs the 3500 and the competition's 2500/250s use. I had one.