OMC 4.3 missing then dies in high RPMs

[The Cintas Guy]

We just bought a 1989 boat with an OMC 4.3 and cobra outdrive. When we bought the boat the outdrive was locked up. We got that fixed and now the boat runs great when its cold but after it warms up it starts missing and will die if I dont pump the throttle. If I stay under about 3500 RPM (and stay out of others wake) it will run fine.It seems to be triggered by hitting the wake off of other boats? If I try to just run thru it, it will die. But will start right back up idle fine and will do it all over again. My boat buddy said rebuild the carb, I did and it didn't help it.(although it was very nasty inside) He then said coil, i replaced it still no luck. Now I assume the boat has sat for some time cause the guy who owned it passed away. I'm not sure how long it was off the water.
Thank You in advance.
Tony