Vapor lock or something else?

[hoodup]

1. 68 GMC with a 350 cid. when its cold it fires right up every time.
2. After its warmed up its not as easy to start.
3. when i open my fuel cap i get a a rush of air and fuel...most times

There was an earlier thread along these same lines and someone made mention of fuel cap issues and fuel line being to close to a heat source.

Ive since changed to a vented cap to see if that keeps me from being kissed with fuel at the pump.

Any ideas why I'm having vapor lock issues? Please help!

Thank you in advance