96 Taurus LX Fuel Odor

[troublemotif]

I bought this car recently. It has the 24v Duratec engine in it. It is very clean inside and out. Aside from doing a major tune-up on it, I have changed the valve cover gaskets, upper intake plenum gasket and the oil pan gasket. I have also replaced a number of vacuum lines as the original lines had become brittle. We had an issue with the check engine soon light coming on. The code was an egr but we fixed that by replacing the vacuum lines. CES is no longer on.
The car is running great!
The only problem that we are having is a strong gasoline smell particularly after a fill up. The smell seems to emanate from the rear drivers side. It is not detectable from the passenger compartment unless driving with the window down.
Is there a fuel tank vent valve or pressure release valve that may be malfunctioning?
Any help would be greatly appreciated.