King pin weight

I'm going to add that towing is not the only use of a pickup truck. I am always worried about stopping, and with something like gravel in the bed, the truck's brakes must stop both the load and the truck. I would be more worried about GVWR in this situation compared to towing a trailer with its own brakes that, if set properly (a big if), should help a lot. So what a truck actually can handle when pulling a 5th wheel trailer depends mostly on rear axel capacity, tire capacities, the combined weight rating (since the drive train should be built to take the GCVWR), and driver experience. That said, my experience tells me that one shouldn't go down long, steep grades without low gears (gas engines) or an engine brake (on diesel engines) to help keep the wheel brakes from overheating, and take corners slower when pulling a trailer. I will admit to knowing little to nothing about legal issues for the different weight ratings, which might also vary by state.

JRMunn