The SLP RS package was different. You could get the "RS" package on any '98+ base model or Z28, but not an SS. The RS was a factory option package called the Y3F appearance package (rear spoiler, side skirts, rear valence, and a goofy looking 2-piece front valance).
http://i103.photobucket.com/albums/m149/CallawayC8/paint%20colors/99brightblueZ28.jpg
That's a Z28. The base V6 version looked exactly the same but had a body colored roof. The '98+ "RS" was an SLP option that had stripes and an SS grille, like gillbot mentioned