[NO_RETURN]

Not to jump to the worst case scenario but have you checked the oil for coolant contamination or oil in the coolant? Just looking at the dipstick is not always going to show it. Also any steam in the exhaust? You said it overheated.... multiple times?... you may have a compromised the head gasket... not a death sentence but a very costly repair. If it is the head gasket stop driving it, you will eventually blow the entire engine.

Hopefully it's just like something with the thermostat or sender. Did you or the shop that installed it use RTV silicone on the Tstat or water pump. The tolerances are very tight and it may have gummed it up. Also the temp sensor / sender should have been replaced too.

However Don't forget to Check the heater hoses as well. I bought a $350+ cooling system rebuild kit for my sons 323 and the one hose not included was the lower heater hose. A day after installing the kit, we found the leak in the heater pipe that connects to the bottom of the tank.

Hope it's something simple... good luck!