magetec

I had some problems last month with the engine shutting down when I hit 4500 rpms. I have since replaced the 3 fuel pumps, cleaned the vst filter, and changed both the engine fuel filter and the fuel water seperator on the boat. Seemed to be working great. This past weekend I was coming in from Offshore and running around 5400 rpms (flat sea) and the engine throttled down to about 1500 rpms but did not cut off as it had in the past. I was able to throttle back up and run on in with no other problems (4800 rpms, afraid to push harder). Could the engine have over revved and throttled back with no alarms?
I have also noticed that the fuel bulb does not remain hard, is this a problem?
I am a new boat owner and don't know everthing that I should.

thanks for the help