Fuel Odors

Can anyone tell me the reason for a raw fuel smell after driving for a period of time. The case is this; I drive the blazer; it runs good and everything is fine but once it has been parked in the garage, a raw gas odor occurs. It gets to the point where basically the garage is filled with the smell. I've replaced the fuel filter, the gas cap is not loose. No visible leaks {under the car}. I was thinking it was the o2 sensors since they regulate gas usage and everything. Someone please just bring me up to date on the situation. the blazer has about 200,000 miles on it; rebuilt tranny rebuilt engine. I'm trying to customize it, put rims on it and the whole nine but that all makes no sense if the car is smelling gasey...haha..

fuel pressure regulator leaking into the intake manifold?