340 CAT ETX intermittent surging with 3000 RPM limit or it'll die and not start

[Broke Pilot]

How would you verify/diagnose the coil???

https://www.bakesonline.com/indmar-h...th-module.html

They can be tested, but it’s not worth it and usually not a reliable test. Usually when you do the cap and rotor you wanna do the coil with it. They’re all wear items.
If it’s not getting enough spark, the ecu may be trying to protect the motor.
You’ve verified fuel, so spark is the only logical item left.
The only other thing it might be on the fuel side is the fuel pressure regulator. It might be dying. Only way to tell though would be to hook it up and scan commanded vs actual fuel pressure. Not sure if that’s a computer or mechanical check though. You said the needle would surge with rpm when you tested fuel pressure.
I’d look at the regulator hard after re-reading your post. EFI usually wants a pretty steady pressure. I’m not sure if these boats use a return style fuel system or not.