Re: Temp gauge and thermostat
Mike, I had exactly the symptoms you describe. I thought it was climate control related but put off checking/replacing it and chose the cheap option of replacing the Thermostat, to no avail.
Still scared by the potential bill, I replaced the next cheapest thing - the radiator, (which on the face of it appeared to be okay).
It wasn't until I got it out of the car that I could see that it was 'shot away'. My car had done around 130K miles when I replaced it.
Hopefully, though, you're problem is the cheaper thermostat one.