WOT limited RPM

[Jtgator]

Bought a 20 ft. Pontoon Boat, 50 hp 2005 Merc. O/B. The boat is very slow, even for a Pontoon and I've had a bunch. The WOT RPM's is only 4000, the manual says it should be between 5000 to 5500 rpm. Any ideas would be appreciated. I' running out of boat money already. Be great if there's an adjustment screw but thats crazy talk...never that easy.
I did check around the toons to make sure no excessive drag and the anchor was in this time....

 

[schematic]

Likely over-propped as many toons out there. Be sure its hitting on all cylinders as well.

 

[Scott Danforth]

its either over-proped or running too deep

 

[schematic]

wouldn't hurt to check the pontoons for water as well.....