Rusty,
I've always heard the reverse, the higher the ply, the less tire squirm. Less tire squirm means less friction and less heat. Another contributor to tire squirm, is the rubber compound and tread depth. ST tires (properly constructed ST tires) have a harder rubber compound and a shallower tread.
I don't like the numbers games that are played by the RV and auto industries. I've never had a problem with anything that is over built, can't say the same when the liars are figuring the figures that don't lie.
In addition to the increase in ply rating, I went from a 235/80 to 235/85 16.
Here's a FAQ on ST tires from the Goodyear web site.
Goodyear RV Tires – Frequently Asked Questions
Somewhere in the flotsam and jetsam from the www thing I have a more info on ST tires I'll try to track it down for you, but this also has some good info on the ST vs LT tires topic.
https://rvingwithmarkpolk.com/2012/1...s-vs-lt-tires/
I'm just putting this out there for folks to do with what they wish. I'm certainly not trying to start the ST vs LT tire debate AGAIN.