P0420 - Hummer H3T alpha

Question

2009 Hummer H3T Alpha. Persistent po420 code, 4 new O2 sensors, all connections in exhaust system are tight, no exhaust leaks or intake leaks everything intake and exhaust side torqued to spec. Is my only option to get a new catalytic converter?
Fuel economy is far worse than the 18mpg highway I was getting & has a rough idle.
This truck from factory runs 2 catalytic converters a bank, each side is $1,200 from GM.

Answer 1

I would check the emission warranty it should be 8 year emission warranty. 

the dealer will replace the catalytic converters under warranty I had my replaced