Why is my2006 trail blazer running hot?
The thermostat is a possibility. If it is not opening to its fully open position when the coolant reaches normal operating temperature, then it could cause the engine to overheat. Probably something that should have been changed along with the water pump. You mention several good possibilities. The important question is does it require adding coolant? Or have you driven it enough to tell yet? Only two ways it would require additional coolant: either it is leaking or it is boiling away. The best way to check for leaks is with a pressure test. There are many places where the coolant can leak internally in the engine or externally, and none are good. Check your oil dipstick for coolant mixing with the oil, a sure sign of head gasket or intake manifold gasket failure.
The sensors could be seen on a scan tool capable of showing live stream data, and should quickly show if they are operating normally or are out of range. Sorry I don't have an answer on how to test the fan clutch-it may be a simple test, too. I'm pretty sure the fan blades should be free wheeling, with the engine off, fan not running.