1996 Chevy Lumina

1996 Chevy Lumina 6 cyl 135000 miles

I Have a 1996 lumina. It starts a runs well. By driving a couple hours and then shutting the engine off. Try to restart engine again, won't restart. While trying to restart I smell some gasoline coming from engine side. After an hour when engine cools down it starts and runs well. When the car is at parking and the engine is running the temparture goes closer to H position. When the car is being driven specially in the highway the temperature goes down on top C position.
I have replaced the plugs, plug wires, oil pressure sending unit, distributor seal.
Any ideas what is the cause of engine not restarting when its hot.