I've got 3 different diffs, 4.08, 3.91, and 3.69 & was trying to test all 3 last year at the strip. So it just happens that I finished on the 3.69, not necessarily meaning I'm going to stay with them...I'm gonna try all 3 again this year and make a final decision on them. I honestly think that the 3.91 are best for the 7at and the 4.08 for the manual 6 speed in the 1/4 mile. I can't confirm this yet because I didnt have everything dialed in like I'd like for consistency.