Electrics/ignition is always suspect when the engine does something hot that it doesn't do cold.

The coil is a reasonably cheap and easy swap. Old coils often misbehave in mysterious ways when they warm up. If yours is old, you might want to throw a new one on. Even if it's not the culprit now, it may be later. It's money well spent either way if yours is getting long in the tooth. Even a klutz like me can change it without a problem.

Good luck.

Jeff