You will need to find out what the existing gear ratio is, because it can have an effect on what gearing can be installed in your existing rearend. The carriers in the 12 bolt rearend are different depending on what the oem ratio is. There is some overlap between the lowest 3.XX:1 ratio and the highest 4.XX:1 ratio. Depending on what you have, it will dictate whether you will need to change the carrier as well as the gears.
