Boat speeding up and slowing down problem? Need help

So my 07 Malibu VLX (300 hrs) seems to speed up then slow down when I am going over 25mph.. Its not extremely noticeable but I can feel it. Almost like its lugging down. Any Ideas? it has only started happening this season. which leaves me to think it is;

A) Trans fluid is running low?
B) Someone mentioned my prop seal (started leaking)?

Any thoughts would help.. I may need to change the spark plugs as a side note.. Its running a tad rough.

That sounds a bit like a fuel mixture problem, but check all fluid levels.

The 300 hour mark is a big service interval for the indmar engines, including full spark plug wire set and plugs, along with all fluids changed. This would be a good starting point if you haven't done the suggested procedures. http://www.indmar.com/service-support/manuals/2007.aspx

i have done a majority of those things, including changing all the fluids.. I will start with the plugs.