I will go look at mine.
I know I have 2 different ratings and you may be correct that there is a load rating only, but each load rating had a different pressure rating as well. The 2600lb wheels are only rated for 65 psi. I will go look and report back if they are stamped or it was discovered thru additional research.
EDIT: Looks like my wheels on have the weight stamped in them. 2600 on 4 and 2830 on the one I bought as a 2nd spare. I don't use the 15's anymore so I gave 1 away.
In a quick search I have found 2600lb 15x6" wheels rate for 60, 65, or 75 psi. Makes me wonder if they are really pressure limited or not.