Ok so my car has been running weird for a while now. I got my remanufactored Jasper motor a while back with the BBK Shorty Headers, BBK Catted X-Pipe plus the mods i already had which are MAC Underdrive Pullies, Flowmaster Catback. Well it felt like my tranny was slipping because when I slowly accelerated the car would studder for a second but then my brother told me it could have something to do with my either ignition not giving a strong enough spark or my emissions or something. well i take it up to advanced auto and get a dyagnostic test because my check engine light is still on *even after gettin the new motor, but we used some of the parts from the old motor to put it back to a "full" motor* and it said o2 sensor and emissions control something. so my dad takes it to the shop and they put it on their machine and it says the same thing. now its gettin fix, but will that really stop the hesitating/studdering problem? what happens if i still have this problem, what all could it be? HELP!