You have only scratched the surface of what could be causing a P0301 CEL.
You've done the basics but now you have to look deeper.
Google P0301 and you will see the L-O-N-G list of possible problems.
When was the last time you changed your fuel filter?
How do you know it's not a bad batch of gas? Just because you "switched back" to a 93 grade does not mean you do not have a bad batch of gas.
And if it was a bad batch of gas, the CEL would not just automatically disappear like magic just because you went up to a higher grade fuel.