See http://www.automotivepartsnetwork.co...product=229679. Also see http://www.bonnevilleclub.com/forum/...e=article&k=38 (from Techinfo).

UIM production date
 

The date on the UIM in there is in June 2003, so it definitely was changed. That would mean there are less than 20,000 miles on it. I also found a sticker in the engine compartment "GM CAMPAIGN -C- Completed" and a dealer code. There are some numbers on either side of the "-C-" that were hand written and hard to make out. Not sure what that means.