Its a long shot because its usually a 3500 rpm alarm, but run the other motor in neutral with the boat in the water. See when the alarm goes off. Its possible you have a bad neutral safety switch. If so the ECM could think that the engine is in neutral.

The plugs fixed it everything is operating as it should thanks for all your help guys appreciate it.

496 mag
 

Hi I have the same thing going on with my 496 mag Replace fuel system including injectors ,dampner, regulators, water temp sensor plugs and wires and raw water seapump and boat wouldn't get past 2000 rpms I'm gonna check out the knock sensor today any other help would be appreciated