Purchased a 50 hp 4 stroke EFI Big Foot for my 18ft Pontoon Boat. It starts on a dime, runs quiet and smooth. Tops out at 5500/5600 rpm, 18mph with an 11 pitch prop. Unless I really accelerate slowly thru the rpm range it will stop at 4000/4500 rpm and hesitate, feels like it's trying to take...