I have an 03 stx bought last year in july. Since then it has started sputtering at about 60 mph and don't drop down into passing gear when I go to pass. I had the check engine light checked and it was kicking out the cam shaft position sensor. I replaced it twice, also replaced the fuel filterand o2 sensors, as of right now there is no check engine light but it still is sputtering and not dropping down. Any other suggestions?