Starting

By hard to crank do you mean slow cranking? The conditions when you problem occurs are what we call a "hot soak" condition. When turning off the engine after it is warm, the temperature of the engine including the starter actually rises for a period of time before it begins to cool off. During this time of "hot soak" the cranking system is stressed to the max, as temperature rises resistance in electrical circuits and components rises. The increase in resistance is most likely what is causing you slow cranking condition. A complete test of the battery, cables, and starter will need to be performed to isolate the exact cause of your problem. It is not uncommon for a faulty starter motor to cause this type of issue.