P0430 code and terrible gas mileage

[moneypitLS]

So I have a 2005 v8 model and recently did new coils and plugs(all motorcraft) and cleaned off my MAF sensor with MAF cleaner from O'Reillys. This fixed my misfire issues and cleared all codes until a week later when the CEL came on for P0430 code (catalyst efficency bank 2). The car drives completely fine, has no loss in power or misfires (no codes or stumbles) the shifts are smooth but im getting like 10mpg right now. Does anyone have any idea what might be causing this or how i would go about troubleshooting my problem? It might be worth it to add that the car has been in a crash and driven for about 30,000 miles with a misfire from bad coils prior to the recent work Ive done so the cat might be dying but I dont want to throw money at cats and find out that it wasnt the issue. Thanks!

 

[joegr]

You need to check the exhaust pressure. You remove the forward O2 sensors (one at a time) and use a pressure gauge in the O2 sensor port to check it. Something like this: www.amazon.com/Tool-Aid-33600-Exhaust-Pressure/dp/B0002SQW9S

 

[moneypitLS]

So I havent read the back pressure with the gauge yet but I got a code reader and found a few abnormalities. I have high readings for my catalyst bank 2 and egr bank 2 as well as my bank 2 secondary o2 sensor reading low. I cant seem to figure out how to upload the video but I pulled up the live data and the bank 2 secondary o2 sensor was reading at .04 volts while revving at 2000 rpms in neutral