Had another blowout on my P rated tires last week. Just left Discount tire and they recommend Carlisle or Maxxis ST rated tires. Neither made in USA. Can't find an American Made ST tire. Which is the preferred tire pulling a rig on hot highways in Texas?

I prefer the Maxxis M8008.

I just had 5 M8008's installed at Discount today!

I have never used the maxis tires on a trailer they make a good atv tire though. My had a set of Carlisle tires on my last boat and they treated me well for several years. I planned on putting them on my current boat and my tire guy recommended a different brand I had never heard of before, he has always been good to me and they were like 75 bucks a piece so I figured I would give them a shot. I have pulled about 4k miles this year and they are holding up great and imo the are alot less bouncy going down the highway that the marathons I had on the trailer before.

Depends on your rig. Single axle or dual axle.
Both you mentioned are Load-C rated. Both are good.
Maxxis maybe a little better.

For a bass boat single axle trailer you might need a Load-D rated tire.

The Maxxis M8008 tires that I installed are 8-ply D-rated tires, but these were 15 inch and not 14 inch tires.

Carlisle makes a great tire.

I had a 3 year old Carlisle tire blow out on me. Replaced ALL of them with Maxxis tires. From all of my research on trailer tires (ST) for RVs to boat trailers, most everyone I've seen recommends the Maxxis.
I had Greenball Tires from a local tire shop on my enclosed work trailer, went from a "C" to a "D" and never had any problems but they did wear a little funny. Not sure why but never had a blowout and I put A LOT of miles on them.

I had real good service from the Maxxis 8008 on a travel trailer and Nitro boat trailer.

I've had good luck with passenger tires on my trailers. (Basscats) if I remember correctly majority of your trailer tires are not recommend pulling over 70mph. I have thought about switching to LT tires like some of the pros

Two boats, 10 years on load range D Carlisle's and no problems.

Changed to Carlisle last year and have been very pleased with them so far!

I check the air pressure before each trip and I very rarely have to add air!

The pressure fluctuates more from temperature than from any kind of leak!

Looking pretty hard at 8 ply 15" Maxxis 8008 for my tandem trailer. Maxxis says their ST's are speed rated Q. However our wonderful govt. only certifies ST's @ 65 mph.

I often wonder why 15" trailer tires are not the norm, especially on single axle trailers where D-rated tires are far more readily available to the general public.

Kumho 857 is speed rated 99mph and I have heard a lot of good things about them. Having dealt with more than my share of blown trailer tires(mostly on my larger trailers like 5th Weel, flatbed...) I will pay a little more to avoid the headache. Kumho will be the replacements on my Ranger Trail when the time comes. BUT the OP did specify "made in the USA" so I guess I can't help you. :-)