I'd suggest getting an AC Delco O2 sensor. Regardless of the age of the NGK. I used a Bosch for 60 days (bought it new) and had to replace it. I'm not a fan of anything Bosch on our cars, and usually like the NGK, but this is now the second fairly new NGK O2 sensor I've seen here that may be suspect.
Part numbers for the O2'* are in Techinfo, just run it through www.gmpartsdirect.com
Much better than dealer price. There is some risk of shotgunning here, but the O2 is the primary cause of running rich 90% of the time.