Garret,

I'm pretty sure it has a vented cap. Without this critical little item it wouldn't run well. I don't know where the truck is stored...maybe inside a garage, but the usual source for the gas smell is the carburetor, especially after the engine is run and shut down warm.

If there are no tell-tale leaks on the ground, the source would be fuel vapors from the carburetor/engine area or a fresh load of gasoline that is heating, expanding and breathing out the filler cap.

Does that sound possible?

Stuart