Like some of the other responses, my setup is almost exact as yours. I have a 2011 Sierra, 3.42 rear end, tow package, trans cooler, WD hitch, short bed crew cab. My trailer is 26 ft (30 ft tongue to bumper), Dry weight 5200. Loaded Im at 6200(ish). Im within all the weight restrictions on my truck (GVWR, GAWR, Hitch weight). It tows comfortably but I honestly would not want to go any larger. I am in relatively flat terrain, but I already believe that when I start doing my westward/north westward treks that I will probably want a 3/4 ton. Im okay for the next year or two and not in a hurry to upgrade, as I feel totally safe and totally in control. I just know that eventually I will want to upgrade the truck.
Mike