Car Shutting Down?

My car has shut down 3 times now, each time it happens is when I am driving at high speeds an then shift into neutral and brake because a red light is coming up. I've noticed that the higher the speed is when I am in neutral, the lower my RPM's are. I'm assuming that my car is shutting down when it goes too low. I'm thinking it may possibly be a regulator issue, but I am not entirely sure. Any other ideas what it could be? I have no corrosion on the battery cables. Any help or ideas would be greatly appreciated, thank you!