2004 Ford F-150 Temperature gauge

I was driving on the highway for about 45 minutes when the truck beeped and the little screen said to check gauges. The temperature gauge showed that the engine was very hot, past the "H" I pulled off the highway and opend the hood. The engine was not hot and even cool to the touch. I continued down the road and it did it again and the check engine light came on and the engine lost power. In order to get home I unhooked the battery and hooked it back up to get the check engine light off and slowly made my way home. I called the local dealership and they said the check engine light would come back on in 50 miles and they could not help until the engine light came back on. I drove the truck about 1500 miles around town with the light never coming back on. The next time I went down the highway it happened again and I had the truck towed home so that the engine light would remain on until I could make it to the dealership. I drove the truck to work the next morning with the light on and when I got off work to take it over to the dealership the light was off. I would like get the problem fixed as I need to drive the truck on the highway but the dealership says they can not tell me the problem until the light stays on. Do you know what might be the problem with the temperature gauge changing to hot even though the engine is running at normal temperature?