Temperature gauge suddenly goes to cold?

This Model has a common problem with the factory coolant eating the gaskets at around 180,000 to 200,000 miles. I had a totally rebuilt engine installed at 205,000 miles and used a better coolant. I now have 225,000 miles. A few weeks ago, a new problem appeared. After driving about 8 or 10 miles the temperature gauge suddenly goes to "cold", and the check engine light comes on. A message comes on that says "Engine Hot, A/C off'. The radiator fans come on and if the heater is on, it starts to blow cooler air. The only way to reset everything is to disconnect the battery and reconnect it. It will then run about 8 to 10 miles, and it happens again. The engine is not overheating, it is about 195 degrees. I can let it idle for over an hour after resetting it and there is no problem.

Only fails after driving 8 to 10 miles. I have a new radiator, water pump, thermostat, and temperature sensor. Today I put in a new ECM and had it programmed. The problem is still there. I have seen several people on your site over the last several years with the same problem. Has anyone ever found the problem?