Well, let me just preface this post with a statement. I have zero PCM tuning experience. While researching a tuned PCM I kind of ran into a wall or two. Let me start with the PCM tuning by a little review by model year for the 04+.
04-05 = plug and play, easy chessy
06 = pop in a 05 tuned PCM (minimal issues like a potentially reversed gas gauge)
07= pop in a 05 tuned PCM and hope for the best, I have read that few people have done. And I’m stressing the word few. From what I recall these installs never go smooth, and involve addressing lots of codes that pop. Unfortunately not many people have been forth coming in their experiences. There was a guy who posted some info on 3800tech, basically a nightmare story that ended in his car running “OK”.
08 = I have never even heard of anyone pulling it off
In my emails with Overkill he seemed interested and confident he could get a tune going for an 08. However I expressed my concern with losing functionality in other areas like my instrument cluster, DIC, remote starting, air bags, etc. Then the whole plan came to a stop. My concern was based on how this old 05 PCM would communicate with the BCM, not to mention all the other stuff. Or if it would communicate at all, since the 08s are the only CAN bus GPs.So I guess my "lobotomy" comment was the potential severing of the PCM and BCM. I have no doubt a tune could be done on an 08, but it wouldn’t be an easy process.