Cat converter

Was getting a p0420 code starting Jan 2021, I replaced upstream O2 per recommendation and ran some treatment through fuel to clean cat, codes went away car drive fine, sept 2021 car ran fine went and got fuel came home car ran fine, next day cranked to go to work temp was 70-75 in Texas and got out of the drive way, accelerated and refused to shift and wouldn’t go over 30 floored. Car died after I let of throttle, hard start following. Got it home car revs ok but goes to low rpm after sometimes dying. Changed plugs, checked injectors, changed upstream O2 again (per recommendation again) and still doing the same thing. Wondering if this is going to be a cat issue and how I should go about testing it. Was going to take off muffler and 1st cat from rear then try it and see what happens then take the manifold cat off of that didn’t work. Tbh I didn’t realize these cars had 2 cays, anyone else notice this. 2014 forte 1.8L