I found this site (I apologize if someone has already posted this) but I think it may be helpful for some owners. If you want to know what your RPO codes are you can easily do so now.
http://www.gm-trucks.com/rpo-code-lookup/
Click the link and search aways ladies and gents'!!
http://www.gm-trucks.com/rpo-code-lookup/
Click the link and search aways ladies and gents'!!