u/Classic-Cod-7952

This has been an ongoing issue. My Altima is misfiring and running rough. I have changed the valve cover, plugs and coils and cleaned the throttle body. For awhile it seemed to run fine, but now it will die after a few seconds when I have it in park or idle and when driving it I can sometimes smell gas. The code its showing for the check engine is P0300 and Auto Zone suggested replacing the fuel pump. I dont want to replace the pump if thats not it. Has anyone had a similar issue? Any ideas on what it might be?