So I have a 2003 H2. I've been in the market for a new PCM, and a visit to the dealer determined there aren't any available. Was having a few random driveability issues, perhaps once a day with either an erratic idle or an occasional stall. Paid the dealer 2 hours labor and they confirmed the PCM is having an issue. Standing with the parts and service manager looking at the screen, PCM number 12582605 is not available. Only so-called rebuilt ones available, but who knows how old the capacitors in them are. During this discussion the service manager noticed some very tiny print at the bottom of the screen. Lo and behold, it states that 12582605 has been superseded by ACDelco 19187507 due to starting and driveability issues.

Apparently there's no TSB regarding this. It affects a lot of vehicles over about a 6-year span. I went ahead and spent the $425 for it plus the one hour of Labor book time. The dealer didn't do too well on it. They ended up spending 6 hours having to unplug each module on the vehicle to program them individually, as it would not behave properly otherwise. They honored the quote for the time. And it does drive like new now.

One of their mechanics commented that over the years they've had many vehicles from that era that even replacing the PCM had no effect on the issues. A lot of people ended up just selling their vehicle in frustration. I looked online and can find no reference to this PCM being superseded. Apparently the information is only on the GM dealers page in extremely fine print.