I have an 06RST RCSB for sale... its even the John A. Moss one 5.3 auto.
the 04-05-06 years where the ones that had the most work done to them from regency. the 07-08 yrs where the bear minimum. rims, exhaust, cluster, wing, and stickers i think.

 

I did not buy my RST new, but the window sticker showed an upgrade of $14,999. There is a long list of so called "upgrades" lol.