Look to the manufacturers towing guides.
Payload weight.
Towing weight.
and start from there.
Weights are determined by what the engineers say the truck can handle.
Payload is all the weight that can be placed in or on the truck , pushing the frame downward. It includes pin weight on a 5th wheel or tongue weight on a TT, It also includes all cargo in the truck, driver, passengers, everything that adds weight to the truck.
Tow capacity is the amount of weight a trucks engine, transmission, driveshafts frame etc can safely push or pull, and all the weight the brakes are designed to stop.
so,,,,
Payload is weight pushing down
Tow cap is back and forth.