Catalytic Converter

Hello fellow Taco lovers. I'm the original owner of my 1996 4x4 3.4L and she has 261,000 well used miles on her. P0420 code appeared a few weeks ago. The Taco was due for plugs and wires and for good measure I replaced O2 sensors as they were several years old. I use all NGK/NTK stuff and have been for many years. I cleaned the MAF and throttle body. I also installed a new PCV and ran a 1/2 can of Seafoam through it. As far as I can tell there aren't any vacuum or exhaust leaks anywhere. I replaced ALL vacuum tubing a couple years ago, but the exhaust is original except for the cat. The P0420 code came back after I installed the new parts and cleared the code with my Extech reader. Every time I clear the code it comes back after 5-7 days or around 150 miles. I don't want to drop big money on a new Toyota cat. I have read many things about different mods people have done. My original cat died a few years ago and I had the shop put in a Walker high flow universal cat and everything has been fine until now. I'm looking for opinions on what path to take next. The muffler is original, but I don't really think it could have anything to do with the CEL...? Go with a better aftermarket universal cat, like a Magnaflow? Go with straight pipe and install an O2 sensor spacer or the O2 sensor simulator? I don't have to worry about emissions. Go with straight pipe and leave the O2 sensor as it is? Go with straight pipe and remove the muffler? Or any combination of the aforementioned options. I humbly and sincerely appreciate any and all advice on how to proceed!

Remember, "It's a dog's life, make it a good one."

 

I gutted my cat last fall And kept o2 sensor in. Code popped up same day. I cleared it and it hasnt come on since...