Our much older 460 did that on very hot days and a hard run. We traced it to the ignition coil. But back on an '83 E350, all the systems were different. The coil that quit on me, was the old fashioned metal-can-oil-filled kind.
Vapor Lock and Collapsed Lines are unlikely on a 1996 since the fuel pump is in tank and all the gas is Pushed under Pressure. That pressure reduces chance of vaporization. And, with pressure, a fuel line won't suck closed. Might swell, burst, or leak, but you'd see it dripping gas. The new lines are pretty rugged stuff.
