It's been mentioned here before.......
Inside the fuel tank, there is a "sock" on the end of the take-up line.
Over the years it becomes clogged and can restrict fuel flow. If the fuel
is sloshing around, it may cause intermittent restrictions on the fuel
flow. It's not any easy task, but drop the fuel tank, remove the sending unit
and pull the "sock" off. Don't worry about replacing it, just put an
in-line filter between the tank and the fuel pump.
Good luck!
Rick