Have you cleaned out the throttle body with TB cleaner?
What about the fuel pump? Get a gauge on it to see if fuel pressure is dropping out at higher RPMs. You can do this right on the trailer.
Worst case if take off the carb and have someone soak it in a parts cleaner. From your description it's fuel related (not air).
Does it die with load or just by RPM? Second question is does it have a rev limiter?
If it dies under load I'd check fuel pressure. Sounds like a dying fuel pump.....
Edit: Don't feel bad, I am traveling a ton and won't get to use my boat much this summer. On Monday I go back over the pond
