The "payload" is also a function of the equipment put on at the factory and the primary limitation is the load capacity of the tires followed by the load capacity of the rear springs, both of which can be easily upgraded.
My GM truck has a 6700 lb axle that is a factory upgrade option. In reality the axle and wheel bearings are rated by the manufacturer, AAM, at 10,900 lbs. so who do your believe? The difference is due in part to suspension components like the springs and the frame mounts and the frame itself.
I have had 4WD trucks that the manufacturer produced using the same components and frame as they used for their 2WD trucks and experienced failures at the frame and at the shackle mounts. These areas could not take the added stress of offroad use. Owners also damage their trucks simply by putting on oversize tires that are much wider than stock and put more leverage on the spindles. Lots of ways to improve the load capacity of a truck and lots of ways to reduce it if one is not careful.
