if you removed the cats completely, you might need mini cats for your down stream O2 sensors.
Something like these
https://www.fvd.net/us-en/FVD111LAMSIM/oxygen-sensor-simulator-minicat-sold-individually.html
You don't have to get those exact ones, there are cheaper versions all over ebay and Summit Racing. I myself used the FVD because I ordered thier muffler as well at that time.