I ran a scan after the CEL came on in my wifes Bonnie. P0135: Sensor 1 Bank 1, Sensor Heater Circuit Malfunction...
What is this? Does it have anything to do with the crazy temperature guage? I replaced the sending unit a few months ago, I discussed the problems I was having with the gauge in another post. I just think it would be funny if it is related, especially aftert his much time has passed.
Any help, suggestions, or ideas would be greatly appreciated.

OK, now I've pulled my head out a little bit... Bank 1 is that the left side of the engine? Also is this the "upstream" sensor? In front of the cat?

Check the 02 sensor upstream of the cat. It'* located on the down tube from the exhaust collective by the firewall.