Hey guys, I have an automatic 2006 Nissan Altima SE-R and it's been acting up since I bought it at 74,000 miles and it is almost at 75,000 now. It will occasionally shift hard, and***** the car. It is becoming more and more common. Originally we thought that maybe where we bought it used very low grade gasoline to fuel it, and that might be causing it (it can take regular, but for better performance i'm supposed to use premium). I have not tried premium fuel although I plan to, but I doubt it will be the cause of the problem. What could be the problem?