This is not really what I would call a difficult tuning question, but wondered if anyone can explain it. I have a 2005 Mustang GT, bought it new. On the differential cover there is a small sticker that says 3.55. In the Speedo section of my tune it shows the rear end gear as 3.55. My son just got a 2007 Mustang GT (he liked mine so much he got one just like it, now we have some great father/son car time). Anyway, the differential cover on his 2007 GT has a 3.55 sticker on it as well, but when you look at the Speedo section of the tune file, it shows 3.31? 3.55 & 3.31 were the two available ratios. I will check speedometer accuracy to verify, but was wondering why the "mis-match", and would it effect anything other than speedometer accuracy if I changed his tune to say 3.55, if in fact his speedometer is off calibration. Just seems odd to me...........maybe just a factory mistake?