I'd be suspicious of an intermittent fuel line blockage of some kind. Small items can play havoc once inside a line. I've seen a stray tiny disc of metal (5-6mm dia.) that somehow got into a fuel tank, then into the fuel line.
Once in the line, it behaved like a clack valve or throttle butterfly. Under power, it spun around at 90° to the fuel line, and virtually closed off the fuel flow. Once the throttle was eased back to idle, it fell back to a position that was in line with the fuel line, and let a full flow of fuel past.