Towed a 5700 lb Tahoe LTZ behind ours with no problems.
The 8.1 has a better towing capacity with the 19,500 GVWR chassis and GCWR of 26,000 lbs than the diesel on the 22,000 GVWR chassis with 26,000 lb GCWR. That is why we selected the gasser even though I really would have preferred the torque of the diesel and the exhaust brake.
Late in the game, just before the Kodiak was discontinued, Thor built a few with the 30,000 lb GCWR. As I recall, the primary change was upgrading the transmission from the 6 speed Allison 1000 to the Allison 2500.