2000 GT won't start....sometimes

This has happened 2 or 3 times now. My 2000 Grand Am GT sits in my driveway overnight. The driveway is on a slight incline. It won't start...just cranks really fast. I assumed it was a fuel related problem. I let the car roll out of driveway in neutral on to the street which is a flat surface. Put the car back into park....then it starts right up. Any thoughts?