Fuel Too Rich Bank 1

[its_sak]

i have a 2003 trailblazer 4.2L 4x4. last week SES light came on. got them checked out and 3 codes came in: 1. o2 sensor, 2. fuel injector problem, 3. bank 1 too rich. i reseated the gas cap and the problem went away for about 3 days. yesterday the light came back on. ive added some fuel injector cleaner hoping maybe the injectors were getting a little clogged. its been off so far. the truck drives fine and i havent been getting horrible gas mileage like some other posts. would it be the o2 sensor if the light came back on? and if so which one (autozone shows one before the cat and after the cat)? and where are they located?