well, Service Engine Soon light came on yesterday for the first time so I took it in to get the codes read.. Oxygen Sensor was the fault once again! This will be my third one I've had in this car in one year.. All of them have been AC Delco too! is there a more reliable brand out there or am I just having bad luck?

Is there something fouling up the O2? How burnt up do the ends look on them?

the oxygen sensors are always pitch black when I pull them out. The spark plugs are also black. It really makes no sense though, I still usually get 28-29 MPG until the SES light turned on, then it dropped down to around 23.

Good gas mileage or no, you're still running a bit rich, and that both fouls up O2 sensors and eventually the cat. Check your MAF sensor and TPI.