I have a 1997 Mastercraft ProStar 119 with a 350 Corvette engine in it. I have recently taken it out of winter storage to find that I could only get about 2000 rpm’s out of it before it “bogged down”. After treating it with seafoam, thinking it might be a clogged fuel filter, I was able to get it to 4000 rpm’s before it gave me no more and once again “bogged down”. I now have changed the fuel filter and the same problem still exists. I can get to around 4000 rpm’s and cruising speed but it slowly looses rpm’s over time and I have to turn off the engine in order to get back up to 4000 rpm’s. I have noticed that my fuel pump is making a very loud screeching loud when running, could it possibly be a bad electric fuel pump?
Sounds like a weak pump that can’t keep up with the engine’s demands under load.