My buddy's truck

Cant figure it out. Runs great, but when he shuts it off and immediately crank it back up, no problem, but if he shuts it off and waits 15 minutes, it wont fire back up until its cold. 2 hot batteries, pmd is good. I'm at a loss. It's seems like the computer is not sending a signal.

No codes.

Crank sensor?
Optical Sensor?

Thanks in advance