Thanks for all the responses. In my personal experience, I've never owned a tow vehicle where the rear GAWR didn't match the tire load capacity. And always figured that optional tires were an appearance upgrade and they would not have a higher load capacity.
On a similar line, when people ask about what PSI to use in their trailer tires, the most common answer seems to be to inflate them to the max PSI on the tire sidewall. I can't recall anyone referring to the sticker on the side of the trailer.
But now I know. Now to explain to my friend that he is overloaded, especially running just 60-65 PSI. The obvious answer is to get to a CAT scale. However we are in a remote area for awhile, don't even have cell phone reception w/o driving 30 miles. But I'll work thru that in the next few days. Again, thanks.