First thing you have to do is find the exact trouble code that it is setting. If the catalytic converter is missing or faulty then it will set either a P0420 (catalyst efficiency below threshold Bank 1) or P0430 (catalyst efficiency below threshold Bank 2). These codes usually indicate a failed or missing catalytic converter or an oxygen sensor that is not responding. If it is an ExaustGasRecirculation code then it could be a P0401-EGR Insufficient Flow. Usually on these cars the valve don't do bad and the problem is usually the EGR Vacuum Solenoid. One way to check it is to unplug it and connect 12volt battery power and grounds to the solenoid terminals and it should operate/click, open/close. This is a common problem on this model.
(Item is called VSV for EGR on picture)
First picture is for a 4Cylinder
Second picture is for a V6
You are not getting an accurate diagnosis by these shops, they are simply guessing.
No do NOT replace the EGR valve, that is not the issue. As long as the car will idle or stall when vaccum is applied to the egr valve then all you need to do here is replace the vaccum switching valve and the modulator.