Car Problem?

well..i have a 97 accord lx..automatic..somehow ever since I installed my DC Sports header..the car's acceleration seems to be weaker..I have to floor the gas pedal in other to get a burst of speed. Usually..i dont have to step on the gas pedal that hard..It might be because I have a messed up spark plug and wire (one of my spark plug wire is loose...so I have to push it back in place) the car runs fine though..just that the acceleration seem very very slow..not normal. I also have an Injen CAI with K&N filter...it might be the air that it sucked in..cause on humid/hot days..the car would accelerate slower..also I often shift from D4 to D3 in normal driving..i dunno if that's also the cause of the problem..So what you guys think?