My '17 Silverado with 5.3 v8 threw the P0420 code two weeks after I bought it as a Certified Used truck @ 31k miles. This code is the same as yours except bank 1. The dealer replaced the "Y" Pipe that has all 3 cats under warranty. It was my understanding that this was a known issue, as the dealer told me they were on back order.
ADDED: For what it's worth, I had just done a CRC GDI cleaning 300 miles before this. You can always run some Cat Cleaner through it.