Code P0420 means Catalyst System Efficiency Below Threshold (Bank 1)?

I have a P0420 OdbII error Code P0420 means "Catalyst System Efficiency Below Threshold (Bank 1)"
I have done the following.

1.) EGR valve taken out and cleaned
2.) EGR Vacuum solinoid tested
3.) Replace the PCV valve
4.) Replace air cleaner
5.) Cleaned fuel injectors
6.) Replace Gas cap
From all the research I have done I believe the source of the problem is in the EVAP system
Can you point me in the right direction as to where to further troubleshoot.
I know it may even be a bad catalytic convertor but I would like to try and diagnose the problem before I replace it, if it is bad.

Thank you
Arod~