I'm trying to figure out what all of those tags mean when referring to the sts.

STS4 refers to All Wheel Drive. 1SE, 1SF, and 1SG are ordering codes (like the famous Z28 Camaro) that denote level of options included. 1SG includes the most bells and whistles. You can find these codes on the window sticker if you have it. They are also printed on a label on the underside of the cover over the spare tire well in the trunk.

Makes sense. Thanks D&D

'Z28' was just an option code? I never knew that.

1SE, for example, includes this:
1SE - 1SE LUXURY PACKAGE: *MULTI-DRIVER MEMORY SETTINGS *POWER ADJUSTABLE LUMBAR *HEATED FRONT SEATS *HEATED REAR OUTBOARD SEATS *HEATED, LEATHER STEERING WHEEL *EUCALYPTUS WOOD TRIM ON CENTER STACK, CONSOLE AND IP *BOSE 5.1 STUDIO SURROUND SOUND WITH IN-DASH 6 DISC DVD CHANGER AND ADVANCE DVD NAVIGATION, INCLUDES TWO FREE MAP UPDATES (REPLACES STD/OPT RADIO) (REPLACES COMPASS IN MIRROR) *RAINSENSE WIPERS *UNIVERSAL HOME REMOTE *AUTO DIMMING ISRV MIRROR (REPLACES STD ISRV MIRROR) *17" POLISHED ALUMINUM WHEELS *TRUNK CONVENIENCE NET

Each '*' separated item has it's own RPO code, all of which are detailed on the infamous build sticker on the bottom of the trunk floor mat.