After talking to you, Mike, so far so good! Thanks for all of your help.

 

With respect to overheat light on when truck cranked cold: See this from info previously sent -

If the engine coolant temperature gauge receives no input or the input is out of range the temperature gauge will read cold and the high coolant temperature warning lamp will be illuminated.


So if you knocked the wire loose off the engine coolant sensor it would do this when truck is cold. See attached pix from RAVE