96 Cav - Trouble Codes PO420 & PO440. Please Help

[oddnyte]

Hello Everybody. I was wondering if somebody has ever had issues like this before and could help. I have a 1996 2.4l Cav. When I go to start it, it hestitates, bucks and feels like it wants to stall. When I pump the gas the car car starts off bumpy but than is great for the rest of the trip. My light is on and the codes are 440 and 420. I have already changed my before cat o2 sensor, got a aftermarket cat a year ago(which I feel may be bad again being I just recently changed the 02 sensor) and have tightened the gas cap for the 440. I don't know what to do and don't really want to get ripped off by bringing it to a mechanic, but my options are slim and the car seems to be getting worse. Any info would be greatly appreciated. Thanks in advance!
Mar