Chevrolet Repair: 97 chev venture wont start when warm, vapor lock, gas tank

Question
Sporadically, when engine is warm, when trying to start it, it goes chug-chug or does nothing & won't start. Usually starts after sitting cold for several hours. Other times, it cranks right up even if warm. Very unpredictable problem. Always runs smoothly. Has 150K miles. Replaced fuel filter so far. We've read some previous suggestions at this site. What is a good sequence of things to investigate, rather than starting with "fuel pump" like a shop recommended? Husband pulled off some sort of line that runs toward gas tank to see if cloggged, it wasn't, he reconnected, then it started fine. What is a "vapor lock" and how to solve it? What is the long box forward of the gas tank?

Answer
Hello EER,
A vapor lock is where the fuel in a line gets too hot due to proximity to the exhaust system or a hot part of the engine, and the gas in the line actually boils, and turns to a vapor. The vapor acts like a spring, absorbing the attempts of the fuel pump, and not letting fuel flow.
That problem is not as common as it used to be, but a pump that isn't pumping like new can be defeated by the vapor.A good pump circulates the fuel fast enough to keep the vapor from forming.
A pressure test may show low.
I have also had perfectly good pumps not put out properly due to a split in the hose in the tank connecting the pump to the fuel line. Again, a pressure test should find low pressure, but be sure to check that little hose while in the tank. Don't reuse it on a new pump, or the same thing will happen.
Van