This has been a popular topic recently, so I'll attempt to write something up that can be referenced rather than adding information piecemeal in response to various questions. What is an O2 (oxygen) sensor? Spark ignition engines must inject a precise amount of fuel based on how much air enters...
dfkitcar.com
You can tune the MAF using the narrowband O2 but only if the computer is commanding 14.7 AFR (staying out of Power Enrichment). Theoretically you can cover a lot of the MAF curve (and the VE table) without getting into PE, but as soon as you do, tuning by fuel trims is pointless.
Sounds like there are still a few things to figure out, like making sure you're getting good MAF readings, but at this point I'd be looking at doing your own baseline tuning vs trying GMS2 vs your as-found vs anyone else's setups. Let us know if/how you want us to point you down that road.
You're going to need a wideband O2 sooner or later if you want to do your own tuning, so might as well set that up now. You can tune for cruising around town without one but you have to have one to tune for going fast.
It's generally inadvisable to use a wideband as a narrowband emulator. It's a less reliable setup and folks have run into issues with the narrowband emulator not responding quite like a real narrowband and throwing the computer for a (bad) loop.