I have a questions:

1) Has the ignition system been checked?

As already stated, your symptoms could be from leakage from a wire(s) or the coil could be going bad. I would call IPD and get an ignition tune up kit, plugs and wires, cap and rotor and replace it all. That may have an effect, or the coil may need to be replaced too. It's not too expensive, call around the USA for it. All of the above are DIY repairs.

You have to be careful not to allow oil or water to run past the spark plug cover and into the wells holding the plugs. Water or oil is conductive, so electricity could leak out of an old wire and ground to the engine, effectively causing a miss, and chugging perforance.

The fuel pump is inside the fuel tank, so it would require dropping it to remove. You could get a fuel pressure tester or have it checked at the injector manifold before dropping the tank.

I would check the ignition system first and do the tune up if it hasn't been done. If it has, then get the fuel pressure checked.