Maximum trailer weight your truck is rated to tow is a warranty issue. It defines the weight that the manufacturer is willing to guarantee it will tow and THEY pay for problems that may occur during the warranty period. Payload on the other hand is a SAFETY issue. That's why the infomation about it is found on the DOT safety plate that is required to be in the door post of every vehicle sold. Other safety related issues are the Axle weight ratings and the GVWR Gross Vehicle Weight Rating. Other WARRANTY issues are GCVWR (gross combined weight rating).
Good luck / Skip