@skidmarkwarrior I really feel for you. Obviously, you are miserable with this heat condition. It sounds as if you have done considerable research yourself, but that is not always fruitful. I had non-alcoholic cirrhosis and prior to being diagnosed, which took around 17 months, I did a lot of research but never hit on cirrhosis for some reason and I'm a pretty good researcher. I know my doctor was working on it too but apparently he did not hit on cirrhosis either. Do you have any other symptoms, even some that may not seem related, that you could add to your search criteria?

I know it's costly but if I were you I would try to go to the best medical center possible. If you need to stay local, have you been to Cedars or UCLA medical center? The most apt cause is thyroid of course but if your thyroid tests are normal that is ruled out I guess, although I have read somewhere that you can have a normal TSH but may need to have other thyroid tests, I don't know if T3 and T4 are those other tests of if there are more. Also, being overweight is, of course, contributing to overhearing. I presume you have tried to lose weight. I know that battle myself, and it is not easy. I managed to do it, primarily because I needed a liver transplant and I knew I would have an easier recovery if I was not carrying as much weight.

I do of course know you, yourself, have researched, but have you seen these articles? I generally rely on Mayo and NIH for health information but I couldn't find anything on NIH and I think HealthLine and WebMD are also considered to be fairly respectable.
https://www.healthline.com/symptom/heat-intolerancehttps://www.webmd.com/a-to-z-guides/ss/slideshow-why-always-hothttps://www.mayoclinic.org/diseases-conditions/heat-exhaustion/symptoms-causes/syc-20373250
I hope you find some help soon, I can imagine what you are going through.
JK