2004 gtp RPM hesitation...need suggestions

hey guys.. i have a 2004 grand prix gtp but over the last month the car hesitates when driving after first start. i just dont know why it hesitates... i let the car warm up and everything.. and btwn 2k and 3k rpms the rpms drops (hesitates) i took it the dealer and they changed the fuel filter and it ran jut fine for 2 weeks then it went back to hesitating. do u guys know what might be the issue? everything on the car is stock, except the air intake. i put a KN air intake on my car. can that cause the car to hesitate? do u think i might need to get my fuel system cleaned? please mail me back. want to get this issue taken care of asap.