Code P1133 back even after replacing o2 Sensor
 

Truck in question is a 2008 Chevy 1500 with a 4.8. The truck has had 3 o2 sensors replaced overall but the most recent one I replaced (assuming it was bad because the other two did in past few years) and code P1133 is back. I checked everything and all of it is still hooked up and nothing looks or feels out of the ordinary so kind of stumped. Weird part is it's been off for a month but is now back and before I replaced it I was just erasing the code. The code would sometimes come back a few days later or it would come back weeks later so I am unsure at this point. All o2 sensors are OEM replacements so I am confident the sensor is fine. I also seen something about the threshhold being too low causing o2 sensors to throw codes so the computer needed reflashed? And what are some things I should be looking at? Any help is appreciated and thank you for your time.

look for exhaust leaks or sensor wiring for obvious damage.
Further diagnosis will require monitoring a live graph from the sensor.

First two things are already done. What do I need to look for when looking at the chart? In the mean time I will look at some YouTube videos to see if I can figure it out myself.