Look for a sticker in your glove box door. You needa factory manual to dechipher all the numbers, or go see the parts person at a good Chevy dealer, and get the numbers decoded. Otherwise, you can always remove the rear end cover and count the theet on the ring an pinion gears & do the math. The pinion gear may even be stamped with the ratio.

 

i came across a great site that you already might know about but it decodes the rpos up to 30 at a time..http://www.camarosource.ca