p0404 and p0420
 

Ok, so my inspection is due, took it to a mechanic and he says I need a new cat, I would like to verify that on my own. I am throwing a p0404 and P0420 code. I replaced the egr valve 2 months ago and immediately afterward i noticed the cars rpms would jump ever so slighly at highway speed, but never did prior. I have my own actron scan tool, but don't fully understand the live data. Are there anyways to tell if my Cat Converter has gone bad? I know the basic symptoms, smell, rattle, cherry red, None if which I have. I was thinking it could be my upstream 02 sensor?
Not to sure though any opinions are appreciated

PO 420 is almost always a bad cat. If you want to look for yourself the look at the upstream and downstream O2 sensor data. If the voltages mirror each other then you have a bad cat. Upstream o2 voltage should fluctuate above and below 500mV always, downstream o2 should fluctuate below 500mV when the cat is working.

Ok im going to post the live data in a bit! Would a bad cat throw my egr off?

Ok So I cleared the codes yesterday, cycled it and the 404 is no longer there. p0420 has come back after 40-50 miles.
Heres a few posts of the live data