My only suggestion would be you try and return it to stock with a used cat and sensor. New cats are ridiculous and HFC and Test pipes will probably only give you a different code. I think the number of people that can switch out cats and test pipes without a problem is like 65-75 percent. Others will have issues. The system is just very sensitive and the differences in manufacters parts cause problems.

 

Well considering the fact that the code jumped sides when the cat plugs were switched. Sort of proves, at least to me, that the cat is the source of the problem

 

I agree it has something to do with the repaired cat or sensor, its now just how far you want to go to fix it.