Why does my car still shake and cut off at stop lights?

I have a 2001 Ford Focus and have changed everything that the Auto Zone codes said including O2 sensors, Mass Air Flow sensor, battery, alternator,and air filter. Prior to working on it, my car would shake and putter at stop lights but never cut off. The check engine light was on and the O2 sensors were changed. That lasted for 2 months until recently my battery light came on and now my car starts but cuts off. The check engine light finally went off after I changed the MAF sensor but why is it getting worse (cutting off) instead of better? What else could it be if the battery, oxygen sensors, air flow sensor, and filter are all new and working? Please help. I'm at my wits end plus my battery light is still on even with a new battery and alternator.