The latest information I got from my Service Tech isas follows.
Now Ididn't go back and read 11+ pages of posts so if I am repeating something, then so be it.

There is a range of Vin #'s that MAY be affected. The Heads that become affected will show a check engine light and act like they misfired.

The dealer service according to GM Warranty service must reset the PCM, nd drive the vehicle again to reproduce the original code, and problem. Then if it occurs, they will proceed to the next step which is to begin head replacement.

My truck, I'm told falls within this range, built in March 2006. I asked why we can't just replace the head, and the answer was that not every truck will havethe problem. ???
Okay, so I am keeping my fingers crossed. There apparantly is something that wasn't perfect in the machining of the head. Now who knows how many pieces of equipment machine these heads. and maybe it was one machine wit hbad tooling. I don't know but it certainly is unsettling.