Please help. First post ever. Stumped.

[Aircrewman28]

2001 F225TXRA twins on a 2001 Grady white express. Starboard motor (306 original hours) will not go above 4300RPM. Starts shaking and vibrating. Runs fine up to about 4000RPM. Replaced fuel filter. Water separator. VST filter. Is it the TPS? That’s my next go. I can’t find a part number for it. Is it called the throttle position assembly for 175$? Heard it was only 40-60$? Don’t want to buy the wrong thing. It did this once before, last month. Turned motor off, fished for a while, started back up and it was fine. It’s now done this the last 2 trips. I have YDS, no codes thrown. All annual maint just done. Added VST filter to try and illuminate. No joy. Any help is appreciated.

[99yam40]

monitoring rail pressure will tell you if there is a lack of fuel if pressure does not stay in spec.
2001 means 19 years old, have you had the injectors tested and cleaned

300 hours means less that 20 hours a year, motor have not run much each year
which is not good