temp gauge running hot for no reason
 

01 2500 4x4 is running around the 215*-220* mark with full coolant, full oil, a 2 year old radiator and thermostat. I can put my hand on the radiator cap and its nowhere near hot enough to touch. There are no leaks from the pump. Could this be the gauge, sensor, or T-stat problem? The replaced T-stat is not Cummins part.

Any help is greatly appreciated in advanced!
Thanks, Caleb