99 S10 PO420 code

I'm new to gas tuning, I have a beater 99 s10 that got a po420 code so I licensed it to shut off the light after removing the plugged cat, but I see it's already shut off but still throws the code? Any help please? I would like to shut off the cat test but I don't see where. Also the truck always had a little surging when cold the first minute of operation and now it's worse with the cat gone. Runs great after 1 minute, O2 sensor? I noticed the voltages are very different between the 2 O2's when cold but very similar when warm. Any ideas? Thanks for your help.