bill190

Basically I do everything you have done, then if that does not work, I spring for a new radiator. I get a larger radiator if I can. Before doing that, you might want to confirm that your temperature gauge is reading correctly. Usually when these have gone bad on my vehicles (temperature sender older vehicles/ temperature sensor newer vehicles), the temperature reads too low. I suppose it could read too high? Anyway might want to get a thermometer and place it on the engine.

Might check your owner's manual, fuse section for a PCM B fuse...

The factory service manual set is around $150. I would think the dash switch would be much less expensive and worth a try first... (And sounds like it will need replacement anyway!)

Well that is the idea behind getting a factory service manual set. This explains how everything works for your specific year/model vehicle. As to the electrical for this, one or more of the books will show you all the electrical components involved with this, and where each component is located. And that is the BIGGIE! Where is the darn thing located? It shows you in these books. Then you can examine the wiring/connections to each thing. In difficult cases like intermittent electrical problems, you can run temporary wires to the gizmo from inside your vehicle and monitor the electrical signals with a multimeter. Then when the problem occurs, you can see if something is getting power as it should or is not. Then test another component if that is working ok. Etc.

If no one has an answer to your question, I would suggest you get a factory service manual set from your GM dealer. This is a 4 book set which gives detailed troubleshooting instructions for everything for your specific vehicle. And being as everything is electronic these days, troubleshooting many things requires the use of a voltmeter and ohm meter (multimeter) to check various sensors, actuators, etc.