Hello, My port motor is running 350rpms slow or behind the stbd motor. Computer scanner says everythong is good. Furl injectors are goong to be professionally cleaned and other filters checked. Any other ideas or experiences with this that the problem could be? Thanks

Plugs.
Those dumb .060” gaps used in 496 trucks got carried over to boats. I’d start with with plugs with no more than .040” gap to start with.

Lower power could also be fuel filters ir even flaking cool
fuel module getting into injectors..

Try a different set of props or swap them for a test run. Just remember your controls will be backward.

got details...
so fuel pump has a pressure regulator (kinda looks like thermostat a bit)...that was made with paint on the inside which ends up sticking to regulator. paints ruins regulator then paint gets into fuel injectors and clogs or can ruin them. Merc replaces fuel pump/regulator and injectors for free. recall warranty, so they are replacing all this on both.
this caused the cylinder to run hot (lack of fuel) gasket area around the bad cylinder and burn it up. everything involving the cylinder is fine so that good.