Were I you, I would also (if you have not already done so) contact GMs district office and apprise them of the situation. Their address, phone number, and probably email should be in the back of your owner's manual.
__________________ "We are forces of chaos and anarchy. Everything they say we are we are, and we are very proud of ourselves!" -- Jefferson Airplane
Dick Naugle says: 1. Prepare food fresh. 2. Serve customers fast. 3. Keep place clean.
I agree with everyone else the scan gauge didn't cause the problem. The only thing it is doing is relaying information that is being fed into the computer. Any type of scan tool when used is only hacking into the computers memory so why would this one be any different than one made by GM or any other manufacturer. I think it would be funny if it was a vacuum leak as Ron suggested. I'll bet the service personnel would never admit it though they would tell you anything but the truth and probably replace something else just so they could claim that was the problem all along. I'll bet that service manager was really surprised to know that you took your concerns to the maker of the scan gauge. She'll probably be more careful what she says and who she says it to from now on. Glad everything got worked out for you.