For a while we ran the OEM GTO Differential with a spool. We initially had 2.91 gears in the car but went to the 3.46 OEM Gears when we went to the spool. The spool was hard on the lower control arms at 800+ rwhp. After encountering some problems with the control arms we decided to go back to a Differential. We chose the GForce1320 Engineering Ford 9 inch IRS kit for a number of reasons including the Wavetrac option offered with a lifetime warranty. The initial setup with the Wavetrac had 3.56 gears. The Wavetrac self destructed on a routine launch, the 4th pass down the track with that unit. Mosier was very gracious but advised me they would only honor the warranty one time, which is not why I bought the Mosier/Wavetrac combination. Chris at GForce1320 Engineering recommended I look at the Strange S-Trac which was also endorsed by Preston Davis, a friend of mine that runs a nostalgia top fuel dragster out of Memphis. We set up the Strange S-Trac with 3.56 gears and we haven’t looked backwards.