We bought a Prime Time LaCrosse 329 last (about 10K pounds lightly loaded) year and the GMC 1500 was overloaded. Powerwise it was sort of OK (it would downshift at the drop of a hat and scream going up a hill) but we were quickly overweight and the truck really squatted. After spending a month of weekends looking around I ended up buying a Ram 2500 with the Cummins diesel and have been very happy with it. Even with a low end Pro Series hitch (not recommended) it does a good job towing as long as you keep the side winds under about 25 MPH. I did just buy a used Hensley and need to measure everything to get the right drop stinger on order.
A friend of mine has an ecodiesel Ram and loves it for most things (mileage, quietness, great torque) but says that it sort of sucks towing his big enclosed trailer (about the size of a 20 foot travel trailer). The weight is not the problem but the big flat nose on the trailer really kills the mileage and 65 is about all it is comfortable doing on the highway. Headwinds really suck. He said that he really wishes he had bought a 2500 with the Cummins.
2015 Primetime LaCrosse 329BHT