Snoozer

I have a 94 with the LT1 engine, today when I started it in the garage it ran fine. Took it to lunch about 25 miles. Left it in the sun for 90 minutes. When I started it to go home, it started and then died, tried it again and same result. After another try got it started and pumped the gas to keep it going. Ran it at high idle for a few minutes and then it was fine. Drove home and left it in the sun again to see what would happen and it did it again. This has never happened before. What do you think is wrong? Temperature if in the middle 80's and sunny. Did I get like a vapor lock? Roy