Can anyone tell me how to check for a bad EGR? I just replaced the cat,plugs and wires. The car runs fine for a while and then starts losing power. The car is a 2000 with a 3800 V6. I had the parts guy scan the codes and got a PO300, PO404, PO756. I havent had the codes rechecked since the new plugs and wires. Any help would be appreciated!