As per my other thread in the AJ-racing forum:

just installed all 3... pickup does seem better, have yet to compare mileage... just a question though... it seems now that when I'm going around 80km/h say in 4th gear and then I accelerate really hard, the car seems to vibrate a bit more.. almost to the point where it seems like it's mis-firing or something like that... it's weird, cuz it goes away once I let off the Gas, and doesn't really happen until I hit 80km/h and above... any suggestions or anyone else experience this?

thought I would get more hits here and answers

 

Is the problem RPM related, occurs in 1st, 2nd or 3rd gear at the same RPM? Or is the problem speed related, occurs only at 80km/h and above? This might help you isolate the problem. If it is RPM related, start removing each component you added until the problem goes away. Isolate the problem.