I am thinking in towing a 15000 LBS GCWR 5th wheel with a 2011 3500 Chevrolet Silverado durmax 6.6/Alison 3.73, 4x4 crew cab LB. The specs show on the TV the max towing weight is 16800 for a 5th wheel...
I saw a 1500 towing a 37 foot Montana yesterday and I gotta admit, took some nerves of steel. Your setup should be fine if you take it easy and don't push it. I assume you have an exhaust brake installed for those down hill runs. Good luck and happy trails....