Hesitation Problem

I have a hesitation problem with my 2000 Grand am gt as well.. I have replaced the fuel filter, mass air flow sensor, air filter, plugs , wires... and it is still hesitating while doing a steady 55 mph with out acceleration.... any ideas??? I think I have replaced everything... Please help...
thanks,
Crappy 2000 GA GT

you replaced everything on the intake side, but what about the exaust?

Bad catalytic convertor, the gm convertors are very crappy and know to be bad. replace the convertor and your troubles should go away, ive been having the same problems but dont have the cash to replace the convertor yet. also replace the o2 sensor on your car when you replace the cat, because it most likely is bad due the the malfuncitoning cat.