GM-GMC: 88 gmc 1/2 ton lwb. pickup v6- 4.3l, soap stone, model truck

Question
i have this truck and the sticker in the glove box is not there and i need to know the gear ratio for that model truck?

Answer
If you look closely at the edge of the ring gear as you clean things up before the new lube, you'll see two numbers stamped in the edge of it, along with a date code. You divide those two numbers and that will give you the ratio. The numbers are the number of teeth on the ring gear and pinion gear.
if that doesn't work

To find out gear ratio without removing the cover: Jack up one rear wheel, mark the drum to backing plate with soap stone or equivilent, mark the pinion flange and housing. Turn the jacked up tire/wheel, 2 full revolutions using the marks to line up, while doing this, count the number of revolutions that the driveline makes and this will give you the ratio.