Yo - thanks, man. I bought an ebay radio for my 2000 Montana - no wonder the guy took 27.50 - the local gm dealers (and by the way there are only 2 left out of probably 10 in the area a few years ago) are not real eager to help - talked to them on the phone, they weren't even clear on the diff between theftlock 1 and 2 (they were asking if I had pressed buttons 2 and 3, etc) and they wanted $100 plus just to look at it - no guarantees. I was figuring to throw in the towel and buy another aftermarket radio.
To get to the point, I found the little eprom you so precisely described, popped loose what I hoped was pin number 8 (check out the link if you are scoping this out), and now it works perfectly.
The cassette player is a little marginal, but I can pull the one from the old receiver - at this point I've had them both apart about 5 times, I can do it like a lrrp field stripping an M16. My wife is totally annoyed with me for spending countless hours on an old radio, but it is such a pleasure when it finally clicks in. The internet (and anonymous geniuses) have changed my life again. Very gratifying. It's a tinker guy think - she wouldn't understand.
Brilliant piece of research on your part - this news must be spread - I see baffled querys about this all over, with the most reasonable responses being "you've got to go to the dealer to get the codes cleared". Which I would have been happy to spend $30, or maybe even $50 to do - if they were half way cool and said, "look, we'll figure it out and if we can't, give us $20 bucks. We are talking 15 minutes (and clean hands) max with a competent mechanic and the data analyzer. But since it is generally such a ream job, I strongly recommend snipping the little wire. And we should spread the good word.
Thanks,
Doc Benway
Harvard '06 (that's 1906, you whippersnapper)
Bob Hill