This is a HUGE thread on this exact problem, do a search and you'll find it, I remember reading something on it and mitsu did testing and 5th gear made harmonics and tripped the knock sensor causing it and they did some kind of revision to the trans or something but I forget what it was. BUT there is a reflash/patch (w/e its called) to fix this issue. It's alllll covered in that thread I just forget the name of it...It's MULTIPLE pages long, I'll search later if no one brings it up in the meantime.