Autozone is great for the free code retrieval, but they are not qualified to diagnose you vehicle or get you the right parts. An O2 sensor is not going to cause a lean code. Here is where to start.

Since you have the code on both banks, a MAF is very probable, especially if you are using a K&N or other oiled filter. You can try cleaning the MAF element with some spray cleaner. In all probability, the sensor is toast if it is the fault. Replace it with a DEALER MAF sensor. RockAuto Auto Parts carries the Motorcraft brand. The other cheaper brands may be tempting, but I have learned that they do not work as well as the original. I have been through several aftermarket MAF sensors.

A misfire will cause such a code, but you would know if you had a misfire.

A bad injector can also cause this code it is true.

However, the most common cause of lean codes was completely ignored by the fools at Autozone, and that is vacuum or intake leaks. The rubber gets old, shrinks, cracks, and hardens, resulting in leaks. Check the areas around the PCV valve especially. The other area is the gaskets on the upper intake manifold. Same story, they get old and shrink and harden. This causes them to leak over time. Most guys on this forum with your code resolve the code by repairing these leaks.

Some will talk of a test where you spray a flammable gas or liquid around the intake. This test has been known to start fires, and has so far proven ineffective at accurately detecting leaks, so don't bother checking that way.