Yes, the King BP station is the only one open there in King, but there are a numerous gas stations open all night along his I-40 travel corridor: In Burlington, Greensboro, and Winston-Salem. And why would he be annoyed about going inside to pay cash, surely he was not planning to use a credit card, being the "great" master planner??
Not that I don't believe Gracie, mind you, but the whole gas in King, and annoyed about having to pay cash makes very little sense. Plus where did he get gas to complete the rest of his trip? The Police checked every gas station between Hillsville and the hospital, and no pictures of JY. That's a puzzle, that has yet to be explained by the PT.
Even the prosecutions estimate of 20.3 MPG, would mean he really could not get past King very far without running out of gas.
22.5 gallons x 20.3 MPG = 456 miles which means he running on fumes when he gets to King and the Gracie sighting.
There is something we and the PT are missing, but JY actually being NG is not among them IMHO. It's just a hole I wish they would have filled.