1986 Ford F-150 with a brand new fuel tank and fuel lines has gone through 4 mechanical fuel pumps in a couple of months.
I put a sock on the pickup tube (was originally missing), an extra fuel filter on the line in front of the pump, etc. They keep going out.
I even put an electric pump on as a stop-gap backup and that burned out after only around 100 miles (it's possible I wired it wrong or something but it seems suspicious).
At this point I am thinking about dropping the tank and completely emptying the gas and checking for sediment or something (but the tank is only a couple of months old!).
UPDATE: The mode of failure is acceleration is increasingly sluggish and the engine bucks, then sputters and dies. Sometimes it will restart briefly, like long enough to get where you're going. Eventually it won't start at all.
I cut one of the bad pumps in half and observed that the diaphragm had become brittle and cracked through.
I decided to pump out all the old gas through the fuel line so I could remove the tank and inspect the inside of it. During that process the diaphragm in my hand pump suffered the same fate. Some of the fuel (that which I pumped out first) was very discolored (dark amber) and smelled like varnish. When I removed the tank and opened it up, the whole thing had the varnish smell.
Absent a better answer, I'm chalking it up to filling up at some pump with contaminated fuel. The truck has been driven regularly, so I don't think the varnish-y gas is due to it getting old while in my gas tank. Maybe it was already old when I pumped it in there.
I refitted the tank and filled it with clean gas, put on one more mechanical pump (these have all been Spectra pumps I believe), and it has been running correctly for about an hour's worth of driving.
We'll see what happens.