Thought to post this here, since GM tech is no help.

I can full reflash an ECM (on the bench) using a new VIN and everything seems to flow smoothly. Without powering down the ECM, if I "check status" with EFILive, the new VIN reads out along with the new OS, Perfect! Now if I power down the ECM and power it back up, and "check status" again, the OLD VIN reappears. ??? The old VIN is still in the calibration window of the tun file also. This is driving me crazy.

I am using Bosch Flasher Pro. Yes, it is updated with latest firmware.

I have noticed this is happening with LLY ECM's and 06-on TCM's. Maybe others also.