A couple of weeks after I got my 4Runner, it threw these two codes.
P0136 - Bank 1 Sensor 2 (Passenger, Downstream)
P0156 - Bank 2 Sensor 2 (Driver, Downstream)
I have found TSB EG005-05 that talks about a design change to the O2 sensors. It looks like Toyota recommends part numbers
89465–35710...