My 85 GSL was building up pressure in the gas tank. Not any more.
 

My gas tank was building up a lot of pressure while being driven. I don't know if there is a vent on the gas tank that is plugged, or what. I know that my solution is kind of ham-handed, but it seems to be working. I drilled two small holes in my gas cap. Now I have a "vented" gas cap. Is this going to cause me problems down the road?

just noticed your rear plate one of our locals spotted that car near the strip a while back ...

I beleive there should be a vent

There is a vent line that leads to the engine compartment, through a vent valve, and into the charcoal cannister.

There should also be a pressure relief valve near the tank, designed to pass dangerous overpressures.

pressure in the gas tank is normal and is an indicator of a sealed system. drilling holes in the gas cap shouldn't hurt anything but i wouldn't recommend it.