Assuming it still has the stock ratio, you could look on the sticker in the glove box and get the RPO code for the axle. I *think* GT4 is for 3.73 gears.
Or you could jack up one tire on the rear and spin it 20 times while someone counts the number of times the driveshaft goes around. Divide that number by 10. It helps to mark the driveshaft with something to make it easier to count.
i had 3.42s in my 95 tahoe. personally i would go out and find a 14 bolt semi float axle out of a 3/4 ton chevy. 88 to 98 will bolt right in. ive personally experianced and heard of 10 bolts grenading. but if you want to keep it try drive train depot.com or drive train specialists. they have gears and master install kits at decent prices. good luck
wow, great pics - and thanks for the feedback. Yes, I was looking at a 12-bolt complete rear on ebay but missed it by an hour.
if i hadn't just dropped $250 on new brakes i'd be very tempted, but since cash is a bit tight, I may just look at new gears.