Next gremiln on the car, when starting cold, the dash says "ac turned off due to hi temp". But, it'* not, the overflow tank has plenty of coolant, and it'* running & driving normally. Also, no reading on the temp gauge. Of course, my first thought is temp sending unit, but these newer cars have a way of the obvious solution not curing the problem!

Yeah, that'* probably the temp sensor gone bad. If you replace it and the issue is still there, not a big deal because it was probably going to eat that sensor soon anyways. Don't skimp on this part, they're relatively inexpensive so not worth fiddling around with saving a buck only to have cheap parts cause issues later.

My wife called me this afternoon, and asked if I'd done any more work on the car. Apparently, it'* returned to normal! So now, maybe there'* a connection issue, or the sensor is deciding if it wants to live or not!

Yep, sounds like it!