ok on my 62 f100 uni has a 292 and a t 18 had a. three speed anyway about a month ago I put a new gas cap on it cause it has a locking and I really hate that well when changed the cap about ten miles later it was acting like it was running out of fuel well I took the gas cap off and it had a ton of vacuum so I assume the venting cap was not venting so I went back to the locking cap and it was fine for like a day then it acted like it was running out of gas again took gas cap off and no affect it has a Holley 2 bbl so I took out a bowl screw and no gas came out so. checked the fuel filter in the pump and it was empty but since it was out I changed the filter . I primed the carb and it started and stayed running thought I fixed it well for like two days it was fixed then again it died fuel problem pulled bowl bolt again no fuel took line off pump inlet and plenty of fuel reprimed the carb and it was fine for like a week and again same thing so I replaced the pump then a week later bam same thing reprimed and good for for a few days changed the pump again changed all the rubber lines checked inside the tank and it's clean and it still does the same thing anyone have any ideas

 

on my Uni it draws the fuel off of the top of the tank through a tube that goes to the bottom of the tank. I found my tube was rusty inside of the tube,sucking air. You might check your tube and make sure it is rust free. Also you could take some air and blow air back through the line to make sure you don't have stuck in it.
I also had a similar problem with a car. after a week and screwing around with it,we found someone had put a plastic bag in the tank. it was floating around in the tank and then it would get sucked up into the pickup. Car would stall and then bag would float away only to get sucked up again and stall out the engine.

 

I took the sending unit out nothing floating in the tank pick up tube looks fine it blows back to the tank fine it only does this when it wants