Slt club CAB, just had both O2 sensors replace

P0420 †Catalyst System Efficiency Below Threshold (Bank 1)

Which engine do you have? If it's a V-8 you have four oxygen sensors, two in front of the catalytic converters and two after to monitor their efficiency. Those are the "messengers". You don't replace them because you don't like the message. The code is telling you to diagnose why the catalytic converter isn't doing its job. Fault codes never say to replace parts, but about half the time that is what the diagnosis will show is necessary.