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Replace the electric fuel pump.
Every time you turned the key you heard the pump motor spinning, that doesn't mean fuel was pumping. Most of the time, these electric fuel pumps never stop sounding like they are functioning, they spin, but the ability to create pressure is lost. Without pressure, they are useless in your boat.
They do get warm when in use. Then they loose pressure. It cools and works again until it gets heated up again. And each time, the length of time it works lessens.
You can see how this works with the use of a fuel pressure gauge hooked to the fuel rail schader valve. run the motor and watch the gauge it will likely remain steady as a rock, then suddenly drop in pressure. It only takes a little drop to decrease top end or under load performance (noticed by you as a lower engine rpm) as it gets worse the engine will bog down when trying to accellerate, start to idle bad and then not re start, until you get no starting at all. But the bump still spins away, it just isn't doing anything.