another o2 sensor question

[Truth Explorer]

My check engine light came on 2 weeks ago for a few days and the code read bank2 sensor2. O2 sensor, I know but here is my question. The check engine light hasnt come back, but my gas milage is sh%%! Like 11.7 mpg! I have 2 new O2 sensors, wich 2 should I replace now? Before cat or after cat? Thanks in advance!

 

[Truth Explorer]

Oky doky!

So I changed the after cat sensors and wow what a difference in throttle responce. I didnt think that would happen but the truck does run better. Ill do the upstream or before cat O2 sensors next week and Ill post pics of the fun I have doing it!