[HUMTECH]

If an o2 sensor is the issue it will be the pre cat sensor on bank 2(right side) If it tends to set in colder weather mostly on cold starts you could also have an intake leak. The intake is a dry intake so if its leaking it allows unmetered air into that bank causing that bank to go lean. If you have access to a scan tool to monitor fuel trim levels, cold start the truck and force it into closed loop operation then spray air intake cleaner around the base of the intake runners, if the fuel trim goes lean your gaskets are leaking. Common on high mileage gen 4 engines. GM has since updated the gasket design to help eliminate future failures.