Nothing.
This is one cool truck. It can pull as much as a semi. It is great in the snow (4x4). I'm sure it can out pull any truck. It is rated to pull 13,500lbs, but I'm sure I've had it loaded to at least 14,500. Even the Chevy 3500 HD with the 8.1 big block V-8. I also like the way it rides. I would buy another one in a heartbeat.
I am really interested in buying one of these trucks, but it would be nice to be able to get a little bit of useful information about it other than it can haul a hell of a lot.