My bil has a bass boat (don't know the year) that has a 150 merc on it. If you stay below 4000 rpms it will runs fine if you go above 4000 rpms it shuts down for awhile.

Way not enough to even think about what is wrong and what testing has been. Start with the basics --- Fuel --- air -- Spark

the fuel pressure is ?

Does it have spark on all cyc ?

Compression is ?

Is the air box restricted or did something get suck thru in the air box into the cyc ?. Believe it or not that can be common. Dirt dabbers is our issue and will take out a powerhead in 2 min. when that happens. Not uncommon at all.

This question and the lack of info is like calling the auto service store and providing very little info - example - Hello ---- My car does not work can you help me out ?

Yes, I understand what you ae saying I was just hoping this has happened to someone and they could say "it is the..." thanks for your help.

Well of the cuff the most likely issue is fuel. You have a restriction,air leak or lift pump failure. If it has two switch boxes it my be the high speed winding's in the stator. With more details there may be more help.