Buddy has a 25 sunsation 454mpi ive replaced the cap rotor module in distributor, plug wires, coil and it still cuts in and out when running 3500 plus rpms it runs good then missis then back and fourth.

Anyone Have an Idea What to try Next.

Do a compression test. Just ran into same issue. Did the compression test found I had a broken exhaust valve spring on #1. Every time I would put boat under load it would pop/cutout. Best of luck

Need to check items like fuel pressure when it is happening. I would also physically make sure all connections are tight and ground posts on the motor and batt. Disconn all the weather pack connectors and inspect then plug back in. Get a socket on the grounds to make sure they are tight. You might have something lose that gets exaggerated at 3500 rpm