IMHO, diesel 2500s/250s are not worth the expense. There is very little price difference between a 3/4-ton and similarly equipped 1-ton SRW truck these days - and you won't have to worry about payload. Forget "dry" weights of RVs (including published tongue weights) - use only the GVWR of the RV off the sticker on the side and calculate 12 - 15% of that for tongue weight for a travel trailer (23% for pin weight of a fifth wheel) loaded. The most common mistake made in purchasing a tow vehicle is paying too much attention to max towing capacity and not enough to payload and rear axle capacity. You don't really know what the truck's true payload is until you've filled it up, loaded all passengers, gear and the hitch, and pulled across the nearest CAT scales.
Rob