Check Engine code P219A...?

I have a 2013 Z71 and I am getting a Check Engine light with code P219A. I searched the site and internet and could not find anything that resolves the issue. Hate to take it to the stealership if it's something simple I can fix.
Background: Started as getting P015A codes, switched front driver side O2 sensor and that cured that code. A few days later, I started getting P219A codes. It would come on, then reset itself after a few days. Seems to be getting more frquent lately. I have a code scanner and seem to be resetting it daily now. I cleaned the MAF sensor, Throttle body, installed new gas cap, ran injector cleaner through, and general tightening of sensors, etc...
Any ideas?
Thank you.

P219A OBD Code Definition:

Bank 1 Air-Fuel Ratio Imbalance

Got that. Any idea of what parts are causing the code?

It's telling you that there is a significant difference between the air-fuel ratios of bank 1 and bank 2. So first I would swap the 02 sensors to see if follows the sensor. Also check the bank one wires to make sure that there is not a short and check to see if a wire is not too close to the exhaust pipe.

If it does not follow the sensor then it maybe something in the engine.