my 2 cents
 

Prop is too big. I have a 24' Python (much lighter boat) with a 625 hp 540 cid motor. After trying many props, my boat likes nothing bigger than a 26 p three blade. I can turn the 26p to 5500 with lots of trim, but with more pitch than 26 the rpms drop dramatically.

And that boat has a really low X I ran a 3 blade 25 labbed on mine with a merc 540 bulldog

I was thinking that but his rpm should increase when he over trims.

you need a 25 mirage + for that boat to even get the nose out of the water..that boat would rock with RT HAND REVOLUTION PROP..http://www.ebay.com/itm/NEW-Mercury-...#ht_2343wt_962

well took it out this weekend and fuel didn't change still 4000 rpms. So this weekend we are going to try some props. A buddy said he has a 25p three blade.
Also I think my oil for the outdrive trim pump needs flushed. the oil foams up when we try it running. I am pretty sure it isn't trimming up while running. When we changed the pump from the old reservoirs they had nasty muddy oil water whatever in them. So we are going to clean it and try some props.

Sounds like the trim rams need to be rebuilt (o rings) or you'll just get more water in them...

Well took it out this weekend. I believe you are right about needing to rebuild pump we tried flushing and it is still air-rating the oil. But a local marina loaned us a 26p 3 blade turbo something prop. Which allowed the motor to turn 5200 with trim all the way down. But this prop didn't look like anything nice which pushed to boat only 57mph . It was horrible on plane and the motor seemed like it wasn't even trying. Thinking maybe 25p rev4.

is the oil foam white/milky?

looks like a lava lamp when it starts then just turns real light color. Lots of little tiny air bubbles. after a few minutes let it settle, looks perfect again.

plastiv bottle? or old stlye..upper o ring sounds like. milky color would suggest rams got in some water which isnt the case...ya, play with some rev 4's from bblades and get it over with...