My port side engine is strong until approx 2900 rpms, will only run faster with the starboard engine accelerating to bring it up. it is good & strong up to that point. Rinda scanner show no faults & the ecm shows 100% power available. Did the induced misfire test to all cylinders & all are firing, swapped out fuel filters & then the whole cool fuel/water seperator modules. Put a fuel press gauge on the injector manifold & it shows a rock steady 44 psi the whole time, even at 2900 rpm's when it stops accelerating. checked the throttle cable & linkages to verify full movement.

Not sure where to go next, thinking about swapping ecm's. Any advice is appreciated

Have you done a compression check and leakdown test?
Any noise in the valvetrain?

No abnormal noises, havent done a compression test. I figured there would be an oil consumption issue or some smoke & a throttle split if that was the case.

Make sure you do not have a fouled spark plug(s). Might be a good idea to change all your plugs if it's been awhile.

all the above..if all checks out suspect the injectors are plugged..send them out and have them cleaned and checked

Might be a good idea to change all your plugs if it's been awhile.