1999 mercrusier 5.0 liter lost power

[herberaw]

I have a problem with my 1999 mercrusier 5.0 liter, a couple of weeks ago i hit something with my prop and messed it up a little but nothing major. I didnt loose any proformance, but when i took it out a week later I i didnt have as much RPM and speed, i replaced the prop with exact model and still have problems, i dont believe it is the prop. All I know is that i am only getting about 3800 rpm at WOT and about 40mph, compared to my 4800 rpm and 54mph. I noticed that the engine will rev up on take off and then loose rpms. Any ideas on the problem. I have checked the spark plugs and found nothing, i also changed the fuel filter. Any help would be great