Supposedly all GM trucks after 96 will require it. However, I see quite a few 03/04 trucks not need it.
I'm sure some will debate this, but it's just what i see, there's really no rhyme or reason to it either. I see variations to the relearn as well despite what the "official papers" say.
I'll send or email docs with the pcm , it's fairly easy to perform.

thanks,

allen