If you are going to be towing just occaisionally in the next 5 or 6 years you do not need a 2500 or bigger.
Get a capable 1500 with at least a 5 liter engins and 6 speed transmission.
Yes you are limited on payload,but do the math. 3/4 ton costs more out the door,fuel mileage is lower than a 1/2 ton. What percentage of your use is going to be towing? Do you need 3/4 ton payload when not towing? I chose to go with a 1/2 ton because I couldn't justify the expense of large truck for the amount of RV'ing I do.