Just thinking, if you've confirmed no vacuum leak what could cause a dead lean condition when the engine's been running fine, AFR good, pulled up to a stop & idling. Something getting hot and opening up an air path, then closing back when you parked for 5 minutes & not opening up later on the ride home, perhaps when it was cooler? Seems a stretch, and can't think what it would be.... or how to find it!

What about something simple, like a piece of flotsam in the gas tank blocking the sock and causing a loss of fuel pressure & drop in the bowls. Seem to recall someone here (jb?) having a problem that only popped up occasionally where the engine starved until shut down, and they found a piece of a brown paper shopping bag in the tank, and no idea how it got there? The paper would block the tank exit, covering the sock but still letting some fuel through, then when shut down would float away to come back another time.

Grasping at straws here. It's an interesting dilemma!