Your truck can handle a 5th wheel load up to 12,000 lbs. with no worries. I would highly recommend one of the kingpins like the ones from Trailair. They make a huge difference in ride comfort by minimizing transference of the trailer motion to the cab of the truck.
The GVWR is based on a calculation the factory does when the truck leaves for the dealer. The load rating is dependent upon the leaf springs and the rims and tires that are put on by the factory. The axle and wheel bearings are rated by its manufacturer at 10,900 lbs. so it will only be the limiting factor with a dually.
This simple concept seems to escape most people. The Combined Gross Weight Rating is a very different number that takes into account the engine, transmission, suspension, frame, axles, brakes, wheels, tires, and everything else in the vehicle. This number cannot be easily changed without major modifications to the truck.
You can add Supersprings or airbags to adjust the load capacity. The truck manufacturers do this with the majority of the 3500 trucks on the road that have only the addition of an extra set of leaf springs to boost their rating.
With a trailer it is easiest to go with the airbags as they enable you to adjust the exact height of the bed for the trailer.
Don't get bogged down in the minutia. If the load of the trailer on the bed of the truck causes it to sag then add air to the air bags until the height is where you want it. Stay within the maximum tow load of your truck and you will be fine. These heavy duty trucks are built from the ground up to tow heavy trailers and this is especially true for the current generation of GM trucks that were beefed up considerably in 2011. Only the 2013 and later Ram trucks compare.
