You might first remove any special tunes that are in place, such as the 5-star tune. (That turned out to fix my problem.)
Leave the chassis battery switch "on" or disable it to be sure it stays on. That will allow you to get long term codes in case something else is going on. That will tell you about long term vs short term fuel trims, and whether it is really running lean. Erasing codes with the battery switch is a bad idea in your situation.
Sensor 2 is attached to the catalytic computer, about the center of it. About $100 from Ford, although there are cheap replacements.
Next maybe look at the cat. They can be ruined by a too-rich rich gas mixture.
That's a start anyway. You'll need an obdII scanner, cheap if used with your smartphone.
Best of luck!
2014 Itasca 27n