It's not vapor lock. Fuel delivery or electrical break down as mentioned. Best way to figure out is not to replace parts, but do a test or two when it won't start. Like spark test and fuel squirt observation. If it was vapor lock, it would start if you put gas down carb throat. If it does not, it's electrics. Not to be sinister but without tests it can be anywhere from a loose wire connection to vacuum lock in gas tank to motor semi-seizing. I assume it starts right up in the morning? Without heavy choking or pumping or long turnover?
Commentary, not aimed at anyone:
To have and own an old truck is fun, rewarding and educational. We need to "grow" with our trucks. We need to use these troubles as a learning opportunity for the long future of ownership. Being able to diagnose it can only be learned by testing and finding the problem. If a bunch of are parts are replaced, nothing will be learned. The post will not teach anything. The results could be satisfactory, however. If it's a hobby of sorts, learn all you can and solve it yourself with suggestions as to what it could be. Suggestions as to what it could be are used by some people to start buying and some to focus testing. Testing results are then analyzed and thought out. A person will never learn to do that by replacement of several parts at once. That's how the Guru's on here got to be Guru's. We can all do what they do with their help. There is no OBD, they are our OBD.
Drive it with gas cap off for a day.
