Don't mind me. . . I'll just keep thinking out loud here as I keep doing research. :B
The load capacity on the stock tires are actually LESS than the GVWR!!!
I found some Carlisle tires here that are the same size and get my closer to GVWR (the PUP is not at max weight):
Carlisle BrochureThe tires I found are Carlisle Sport Trail st185/80d13 (product number: 5193531) with a load capacity of 1710 lbs. each.
My BIL can order
Triangle brand (never heard of them) that are load range C, so I'm not really interested in those.
He also has:
STC High Run Boat Trailer Tire st185/80d13 at 1730 lbs. each
Any experience with Triangle or STC? Thoughts on Carlisle?
I'm feverishly doing research as I'm posting this stuff. I'm having a heck of a time finding 13" tires with a load range E, even in ST.