2003 - Impala, loosing pick up ability

Hello everyone, This is my first time here. here is my problem. My car seems to be running really slow even I push Gas paddle all the way. Once the car stops at the light, it doesn't pick up but it takes off 5 miles an hour and it start running little faster as it goes ahead. I have changed the antifreeze, Radiator cap and thermostat. Yet the problem still there. Can you please tell what is wrong with my car? I just had Advance Auto scan PCM and they gave me two codes, PO-300 & PO-404. Any Ideas?

P0300 Is: Random/Multiple Cylinder misfire detected.
P0404 Is: Exhuast Gas Recirculation Circuit Range or Performance Problem.

Seems like Something is wrong with your EGR system.

Either clean or replace your EGR valve. Also it never hurts to get a tune up. New plugs and wires, new fuel filter, and maybe check the O2s.