[ChevyTech]

Do you mean RPO codes which are on the sticker in the glove box?

PRO = REGULAR PRODUCTION OPTION

Here are some sites for looking up what the RPO codes mean:

http://www.geocities.com/n1qcr78/rpo.html

http://www.wiu.edu/users/muwtj1/rpocodes.htm

http://gm-trucks.com/home/content/section/4/30/

http://www.c2e.biz/rpocodes/