FIX for S6 getting stupid hot (85 degrees celsius)?

So, i very well may have a defective unit, my galaxy s6 gets very hot very fast. A few times a day i reach 85 degrees celsius and the phone shuts down and restarts. I think that therm throttling isn't working anymore on my S6. The bad part is that my warranty is void (flashed custom rom from day one). I tried every fix possible (clear cache, safe mode, factory reset, different roms, etc) but no luck. So, to protect my phone i decided i do the unthinkable: undervolt and underclock my cpu. Or enable some sort of throttling for my CPU. I am using the latest version of XtreStoLite ROM, with unified kernel. I need help! HOW TO underclok and undervolt my cpu? Do i need another kernel? Do i need another rom? Is there any secret menu to enable thermal throttling like in LG phones? Please someone give me some info on the matter...