I've seen the reply by Chris with the CVN number. I understand what it does and how it cannot change unless there's a modification in the parameters of the tune.
None the less I'm hearing rumors from famous shops that GM now has a way to find out if the ECM has "ever" received a tune, even if the ECM was then reflash with the stock GM tune.
If I could get some feedback from the pros about this "rumor" that would be great. (although I think those shops were talking about the CVN...but I could be wrong)
thanks!