GMC Sierra 2500 Towing Capacity

For towing a 5th wheel RV, most trucks run out of payload and rear axle weight well under the tow rating. 15000 pounds of loaded weight, which is close to 13k dry will have about 2500-3500 pounds of pin weight. Then a 250 pound receiver in the bed, driver, any other people and cargo in the cab and bed.

Diesel 3/4 ton 4WD crew cab GM trucks have about 2200-2400 pounds of payload. Gas equivalent closer to 3000 pounds.

Short version: 13k dry 5er, get a dually.