Update: Redid the thermal paste, works without a problem. If anyone else comes across this same problem, be sure to redo this as the first step, even if it was recent.
Other things I did before the problem was fixed: bios update to .4c1, windows updates and optional updates, reset power pins, bios update to .4c3, downloaded MSI afterburner (-200mHz core clock doubled time to crash (5 to 10 min); -300 mHz and -10% power prevented problems as well), reset thermal paste and tested at full core clock and power and had no issues for hours.
Common problems are common, so be sure to deal with those first!