Driving truck and all of a sudden the temp. gage will show the truck is hot and when you pull off road shut engine off and start back the gage goes back to normal. Have checked temps. with a light and all are normal. Could the sensor be going bad. The water pump has been changed and new thermostat installed. If that is what it is where is sensor located

 

sensor is located in what would be the lifter valley, basically behind the alternator under the intake on a cylinder head.

 

Does that sound like this could be the problem? The air conditioner shut off when this happens and the truck is not hot. Is this a big job to swap out?

 

Air conditioner shuts off because the PCM sees the temp is to high on the engine and shuts it off to try to save the motor. If the coolant truly isn't hot then the sensor could definitely be an issue. Very easy job actually, you maybe able to slip your arm between the alternator and intake/head and remove the sensor or you may need to remove the alternator (which is also very easy)