RPM drop.

[mytmic821]

I have a 2006 150 4 stroke left hand screw. When it is cold it runs ok reaching about 4300 RPM. Once it heats up it will only get up to about 3700 rpm and then start dropping down to about 2200 rpm. If I take the throttle and oscilate it up and down I can maintain about 3700, but as soon as I stop it will drop. What is this? The engine has about 1600 hrs on it and is maintained regularly.

[rodbolt17]

classic symptom of fuel rail pressure drop.
test rail pressure.
when was the last VST filter cleaning??