I have a 2006 V6 mustang. I had a true dual Hpipe exhaust system installed about 2 years ago. No issues.
I recently had this code about a month ago. I installed all new O2 sensors and the code went away. I just recently drove about 100 miles, got home then boom light came back on. And is showing me the same code.

Currently I do have a leak coming from my valve cover gasket.
(Not sure if that is related)

Code is p0420

I know there are threads about this if any one could shed some...

Engine code P0420