Randomly shuts off

I've had the problem twice now, and I don't really know what to do about it. This has happened twice now. The first time it happened was last year just before I put the car away for the winter.

I was driving it, everything was running perfectly and then the AFR gauge would slowly lean out and then it would die. It won't start, and doesn't get fuel. I had to get it towed him that night, as soon as I got home it fired right up like nothing was wrong.

The same thing happened last night, ran perfectly fine for a half hour of spirited driving then died, so it happened in a parking lot so I just left it there and went for dinner. As I got back it started right up like nothing was wrong.

What would be causing this? Vapour lock maybe? Had lots of gas in the tank both times, new sender, clean tank, new lines. It's a Holley mechanical fuel pump, fuel lines routed away from heat as much as possible and there is a wooden spacer under the carb to help with heat. My only thoughts are that its the winter gas we have here, it never happened all summer even after an hour driving in 30 degree c days.