If it is an 07 and it does not have an extra $100 for the 3.55 Limited Slip axle, then it is a 3.31. The other way to confirm this is to crawl underneath the back and look at the tag that is on a rear axle cover bolt at the upper drivers side. If it says 3L31 it is a 3.31. If it says 3L55 then it is a 3.55.