After doing a lot of research, I discovered that we have four diffs to choose from, stock, 3.42, 3.73, or 3.91. they come out of the cts with the 3.6 liter engine or the srx. all you have to do is switch the yoke and cut off an inch of the steel tip. The acceleration increase will be very noticeable. I'm punching it from light to light non stop. Lost a little off the top end but I don't spend a lot of time above 150 anyway.