2003 Mobius LSV misfire, replaced a lot already

[rothda1011]

The problem starting showing up originally only under high loads like pulling a wakeboarder out of the water with full ballast, but is now happening during normal operations sometimes. What's frustrating is that it will run great sometimes in all conditions and then for whatever reason starting missing. It does not ever seem to happen right away, but after some use it now will always happen. It's getting worse too - last night it was missing while just cruising around at 20 mph. It does not seem to be RPM related at all. When I say missing I mean you can hear it and feel it - it is quite pronounced.

Here's what I've done. Replaced plugs, wires, coil, ECM, distributer cap and rotor, fuel filter, fuel/water filter, completely drained the gas tank, added heet and sea foam. I purchased a MAP sensor from Amazon that was obviously not the right part as the boat would not even start with it installed, but given it starts and runs fine most of the time with the existing one installed I've mostly ruled that out, but I could be talked into trying another one. I've also checked the fuel pressure - it's a solid 30psi all the time.

If you were me what would you try next?