06 CTS chugging on heavy acceleration
 

I have a 2006 CTS 3.6 motor auto trans. 141,000 miles. When I accelerate quickly the car chugs badly. I am not sure where to start. I have never run into this problem with any other vehicle. I thought about changing the fuel filter and go from there. Any help on this would be a life saver.

oh and a side note. The check engine light is on and it needs a right side behind the cat o2 sensor. Other than that the car is awsome. I have done nothing yet to fix the problem. It does seem to misfire every now and then. thanks