Even with a 10 micron fuel/water separator, some stuff gets by. One item that needs to be serviced that might cause you low RPM's is the VST filter. On the port side under the intake induction tubes is the VST tank. The high pressure fuel pump is in the tank. At the base of the pump is the screen that is the size of your pinky nail. To get to it you have to remove the tank and open it. You'll need a new O-ring type gasket. The screen can be clean with solvent and blown with high pressure air. Here's a view of the tank and components.
http://www.boats.net/parts/search.ht...JECTION+PUMP+1