What is your WOT RPM?

I've been down this year to 4700, last year 5000.

Like already mentioned, too much prop. You should be propping for 5200.

So the same boat performs much better with the same prop, and you lost 300 rpms from last year? I know you scanned your engine for codes, but that doesn't mean it is ok. Codes do not always grab mechanical failures.

How many hours are on the engine?

Have you checked for leaking headers?

How old is the fuel? The 525 knock sensor will retard timing if you have fuel issues, which in turn will lower power. This can happen without a code.

Around 70 hrs., this is 2008 and knock sensors I was told are not used on the newer 525's. Had engine on dyno last spring and made good power, put back in boat just like it was last year. I check fuel pressure is good. Fuel is new, topping it off tomarrow. Headers where ok. Pulled plugs all look same, to me they looked a little lean.

You need to prop down and get into the peak HP. This will also help you with planing out. Try a 24 or 26 you might also gain some top end.

And I would try to find out why you are losing 300RPM. Nicks in the prop??