Last year, at 105,000 miles I had the transmission drained, filter replaced, and refilled. This was not a flush, just a drain. I did this after getting into my truck after it had been sitting in a hot parking lot and when starting up, the overheat light came on. The other day I was putting my boat (a 14 foot sailing dinghy that weighs 300 pounds) into storage and after pulling forwards and back a couple of times to make it around the corner into the garage, the light came on again.

I have heard that the sensor goes bad, do you think this is what is going on? I am not low on fluid, I did check that.

 

There are two sensors, wired in series. One in the trans cooler and one in the transfer case. Most likely one sensor is bad. You can disconnect the one in the trans cooler quite easily, the connector is mounted at the top of the radiator on the passenger side under the top radiator shroud. Disconnect thatn and if it is still on you will need to disconnect the transfer case sensor to test it.