There's a guy out in Rowlett named Todd Kirby who runs a shop out of a building on his property, been there for years. Very highly recommended and very well regarded in the Polaris community. It'd be well worth your time to make the drive to see him. 972.896.1002 I've taken 3 bikes to him over the years, and he's always done me right.
This. X2.
If the radiator fins are plugged / blocked nothing will work until it is cleaned thoroughly.
If an 800 over heats just a couple times it usually wrecks the water pump, I have seen one or two thermostats stuck closed but they heat up fast, like 60 to over heat in 2 - 3 minutes.