This is essentially the same as my test as my video checking the rear axle ratio except we are doing the front here. This is just so easy to do with a video!! The Trailblazer/Envoy has 3 options: 3.42, 3.73, and 4.10. So if you do this test and your driveshaft turns like 16.4 turns... you got 4.10 gears. If the driveshaft turns a little more than 13.5... you got 3.42 gears.