Drove to Cali from Nevada this weekend. Stopped and filled up at a chevron in Baker. Got to LA and when I woke up the next morning car was stumbling BADLY and threw a CEL on a cylinder 5 misfire. I'm confident the gas has something to do with it. I use Chevron occasionally in Nevada and never had this problem but I'm sure something was up with that stations gas.
I know it sounds crazy but try using a different gas station then you normally do. Worth a try considering all the other effort
Edit: Also worth noting is that thru that entire tank of gas I was having idle problems even after oil temps where at 240
Since going thru that tank and filling up at the Shell I normally do idle problems went away