Look in the glovebox at the RPO codes (huge list of factory reference codes as to what parts were installed on the vehicle).GU2 2:73 ratioGU4 3:08 ratio GU5 3:23 ratio GU6 3:42 ratio GT4 3:73 ratio GT5 4:10 ratio GQ1 Open Differential Rear Axle G80 Positraction/Locking Rear Axle Different Dash? Try these places and ideas. You can also look on the rear end. It will be on the passenger side axlehousing just inside the leaf spring perch on the front side. Take the VIN number that is on your vehicle title to the local dealership and ask them what gear ratio is in your rear end. If you can't figure it out you can always remove the rear cover and count the # of teeth on the ring then the pinion. Then divide the two numbers and that's what your gear is. If your ring # is 41 and your pinion # is 12 divide the two #'s would be 3.4166666666... Round it off, it would be 3.42 rear. Other Questions? Will all Blazer/S10 rear ends interchange? Answer: Yes, as long as you install a 2wd rear in a 2wd or a 4wd rear in a 4wd. Reason: 4wd rear ends are longer than 2wd rear ends. Are all AWD and 4x4 rear ends G80-posi lock? No, there are many trucks that are AWD and 4x4 that came with open differentials.