Have a 97 four Winns Unlimited 191 W/Volvo penta 5.7l gl. Carbureted, Holley 4bbl.

Question is... Starts, runs fine. When I get past 3/4 throttle the motor hesitates and slows down.(42mph) It doesnt sputter or want stall, just slows rpm and speed. I will pull the throttle back to 3/4 and it will take off to about 50mph. I have new fuel, fuel filter. Plugs, wires, and distributer all look good and fairly new and clean. Previous owner said last year. I still plan on changing them. It sounds and feels like a fuel delivery problem to me.
I understand this has a broad range of possible problems. I am looking for some ideas that may have completely passed me by. Thanks

I had a '96 5.8l with fuel injecton (Ford 351) I had the same issue and was told the cap had hair line cracks causing arc to jump around. Mechanic changed the cap and never had that problem again.

distributer was fine. I rebuilt the carb. Took away the hesitation. Thanks