For a SWR truck, depending on the exact size, tires will have a load rating of about 3500#, 7000# for both tires. The base weight of the truck will be about 3500# on the rear axle, leaving about that same amount for cargo.
Yeah...some seem to think those big 4000- 44xx lb payload stickers on some 350/3500 srw trucks is what we use for carrying a truck camper/heavy GN or 5th wheel hitch loads....and ignore the trucks rawrs. Those big payload sticker numbers come from the newer gen high gvwr's but the truck mfg's are still using older gen 7k-ish truck mfg rawr.