The GM replacements are not as good as KYBs, and cost more. They are not as good as Bilsteins, or Konis, but they cost less. Some new style GM shocks are pretty good, but not the ones for "old" cars, like ours.
I got some from the GM dealer for less then wholesale, around the price of gmpartsdirect.com so I picked them up.
I asked for real Bilsteins, but the parts guys aren't as "knowlegable" as some people, so he ordered these, so i'll try them out (for my 15k mile basis) and get some real Bilsteins from autozone or something
They've been carrying them as a special order item for years. They really can get almost anything special order, you just have to know exactly what you want, and there's no shipping charge.