My 2005 in the same configuration had a 14k+ lb FW tow rating and and a 12.5k lb TT tow rating. I regularly towed an 11.5k lb toyhauler and I also carried a 4K lb truck camper while towing an 8k lb enclosed trailer.
Once you are over 6k lbs on the rear axle, it needs some suspension help. Once you are over rear tire limits, it will handle more with 19.5" wheels. The TC and enclosed trailer tongue weight was typically 8k lbs on my rear axle. I had the truck for 10 years and did not have any problems putting 1k miles a month on the truck this way.
