OBDII is going to be very sensitive to problems with the O2's.
With OBD I, cars might go 100,000+ miles without a O2 code even though the
sensor was worn out beyond use.
You didn't mention where the replacement O2's came from or what the exact code
O2 codes can be from bad or contaminated fuel, plugged fuel filters, vacuum
leaks, bad catalyst and other things. Don't condemn the sensor until your sure.