Yeah, just google rpo decoder, and you'll most likely find what your looking for. The rpo codes are sort of the build recipie for your truck. The engine, tranny, color, interior trim package, etc. are all identified in those codes.
Gear ratio codes start with a "G" (except G80, which is locking diff). Most non ZR2 Blazers had 3.42 gears which is GU6 IIRC.
Oh yeah, and LMC has a nice vin decoder....