Thanks, they're all reading between 77.5 and 79 today so I think the problem is solved. Seems like the second heater was causing the issue. I have another controller being delivered today or tomorrow, I'll turn the second heater back on once I can get the controller on it.
I'll keep a close eye on it over the next few days. Thanks again for the help!!
Awesome. Some heaters have a calibration ring so you can adjust the temperature dial against the actual temperature, but 82 isn't drastic. It'll give you a margin of safety if ever the controller fails too.