I had an overheating problem in my '97, found one bolt on the thermostat housing had stripped out. Removed the intake manifold(s), replaced all the gaskets, re-tapped the bolt hole, then re-installed. Put in new coolant tank, new radiator, new thermostat, new temperature sensor, the works (even a new cap).
All of the connectors, and there are quite a few, are back on and snug.

Ran it a few miles and the temp reading won't budge above 100. Changed the thermostat again and the temp sensor again, still no reading. The upper hose is good and hot but the lower hose is lukewarm at best. Heater hoses are hot and heat is working. No symptoms other than reading 100 on the gauge.

Ideas are welcome !!!

 

maybe the temp sensor...

 

There are two temp sensors, at least on my '95. One by the thermostat is for the engine's computer to determine fuel trim, etc. The one in the driver side head goes to the gauge. If you have access to a scan tool that will show live data, it can show you the temperature that the computer is seeing.

I would suggest thermostat stuck open, that happened to me. I never could get that thing to reach operating temperature! But since you've replaced it twice, I would rule that out.

 

You guys are brilliant !

I found the sensor on the driver's side head and the wire connector had popped loose.

I'm back in business and eternally grateful. Sending a cold one your way...