1999 Pontiac Grand Am my car misfires

Engine Performance problem
1999 Pontiac Grand Am 4 cyl Two Wheel Drive

hello, my car misfires and runs rough then at mid range it smooths out I change o 2 sensors upper and lower change spark plugs ignition coles fuel filter regulator and cleaned throttle bore and throttle body air mass sensor and the car stills runs the sames please help I dont what eles to fix some one told me it could be fuel pump that will cost me another 200 I hate to do it if that will not fix the problem. What is there to do next? Thanks