I always thought that cargo was any item in the truck (people, dog, gravel in the bed, tongue weight, pin weight, whatever) that made up payload. Never knew there was a difference between payload and cargo rating. Too many numbers with too many meanings for most people I think.
To me, the only numbers that mean anything are GVWR, FAWR, RAWR, and GCWR. When weight ratings become a concern for whatever reason, the scale is the only answer.
For a read that includes explanations for all of the acronyms that we commonly run into, check this out from
Curt.