2010 Silverado 5.3, timing over advanced or performance on bank 1. Also code system too lean on bank 2.
When the truck first starts it smells way rich, if you shut it off in the first 5 seconds of starting the truck will delay shut off and back fire slightly.

Replaced the mass air flow, also running very clean and correct weight oil, always kept oil changed.
The truck seems to be getting bad mileage, but runs fine down the road after a 10 second warm up.

It does have an exhaust leak upstream of the 02 sensors I believe. I have a scan tool and am a novice home mechanic. Don't know much about the freeze frame or how to use it. Willing to try and troubleshooting. Thanks for your help

The upstream exhaust leak is causing the lean code. If the O2 sensor sees a lot of O2 in the exhaust stream, it tries to dump more fuel to compensate. But the problem is, its dumping fuel into a system that'* already working fine, thus the rich fuel smell and backfiring.

Fix the exhaust leak the right way, clear codes and retest.

Had exhaust leak fixed, cleared codes and still getting same "too lean" codes on both banks. Which sensor determines this code? The O2 sensor? Maybe I need to ohm the sensors and make sure they have voltage going to them.

I think its time you should take this to a shop and have them diagnose this. This appears to be too far out of your league to diagnose and you obviously don't have the proper tools to diagnose.