Replaced the battery Brand new? Unlikely to be battery if that's a new one and because it happened while running. But measure battery voltage at rest, while cranking and at 3,000 rpm. Then measure battery voltage when the problem recurs. Recovery after a pause could be fuel starvation from an air lock, but running OK at high engine speed is against that. Check by removing the filler cap when it happens: does the running improve and do you hear an inwards whoosh? Check connections on feed to ECU and all earths for that and the engine: disconnect, clean, inspect and reconnect. If those don't show anything I think you're into checking the throttle position sensor and wiring. Visual inspection and wiggle the connections while we're waiting for the experts on diagnosing that. Jonathan