I had the car scanned I got P0137 bank 1 sensor 2. It said it was the O2 sensor and it was a low volt. I am pretty sure that my car is running lean because when i had my car dynoed about 4 weeks ago it was at 13-13.5 A/F. I know I have 4 O2. I was thinking it was the 2 in the front because those control my A/F ratio. Should I use ACDelco brand O2 or another, because I heard people have bad luck with O2's that are not OEM. Any help will be appreciated.

 

You need to back up and read what you wrote. "P0137 bank 1 sensor 2"
That is the drivers side post cat sensor and has nothing to do with your air fuel ratio. It just reports whether your cat is working or not.
And yes I would stick with GM sensors.