Engine will not turn over when hot, i.e. when driven and then parked.

Went to store at 8:15PM - 4 miles, inside for 20 minutes, came out would not turn over in Park (just a single thunk behind dashboard), but started just fine in Neutral. So that kills my idea that it might be heat related resistance in the starter motor or other wiring. Going to check the alignment of the Park/Neutral Safety Sensor in the morning , Monday 6/19/17.

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Rechecked the alignment of the Park/Neutral Position Safety Sensor, and it is aligned. Found no loose or frayed wiring to the starter, and when the engine is cold, the truck starts just fine, and when hot and I turn the engine off, will start right up again in both park and neutral. Wait 45 minutes, turn the key to start and I just get a 'thunk-ah' noise from under the dashboard in both park and neutral. Wait a couple of hours and starts just fine.

After vehicle is parked parking for a few minutes > Engine 'heat soaked' failing starter motor is still suspect .... Heat further aggravates - amplifies failing (old and tired) internal starter components.