Are you trying this on the water or off? (with load or no load?) I had same problem last year after putting new heads on. Trying to take off and plane the boat. 1,800 rpms But if in neutral revved up to rev limiter. My issue was not enough fuel in my table for different set of heads.

This is a long shot but with todays ethanol in the fuel, it causes the fuel lines to brake down and cloge the fuel injectors. It happend to me only it fryed my head gaskets :(

Swap the dist from the good engine and try. Chased a similar problem and it was the distributer

Taking it back to the marina, letting them deal with their mess. Will let everyone know what they find.

Replacing motor. Will let everyone know what's inside

If this is a EFI engine pull the knock sensor wire of the sensor and if it revs up, its either a bad sensor or there is a knock

Wow, can't count the issues. #3 piston dinged up to hell. Rust on the inside of motor, WTH!!!!? New motor goes in tomorrow!!