try using the trim button a bit more , some boats need constant work with the trim button to get the best out of them.
example: i had a 15 foot ski boat with a tricked out F80 four stroke out board.
i was constantly correcting the trim to keep the load on the prop, too much trim and cavitation , to little and the boat went slow, just right and it would chine walk @70+.
the foot throttle and trim buttons on the steering wheel i fitted made the boat so much better to drive.
your 383 s are probably 350 + hp per side so expect some prop slippage on a heavy boat if your trim is not set to suit acceleration.