 If it fires right up, I'm sure it's fuel. But then what you're probably going to have to do is add some fuel pressure to it to avoid this problem. And with an older car like that, they just weren't made to drive in parades. They were made to drive down the road and stay cool. So what you can do... I had an old Mustang that I had a problem with. It was doing the same thing. It would vapor lock.