6V92's TAB lack of RPM

I recently bought a Californian 42' flybridge with low hour 6V92 engines @ 550hp. Engines rebuilt at 1500 hours and rebuilt again at 3000 hours. Second rebuild because of glazed cylinder walls, from what I have been able to deduce.
Last rebuild appears to be a quality rebuild by a knowledgeable Detroit guy in 2007/2008. Engines have about 400 hours now. Start right up no smoke. The last cooling service was about 5 years ago. Other recent service is not documented.
At the time of sea trial the engines ran up to about roughly 2150 rpm+- under load. These engines are rated at 2350. Light fuel, light water, little personal effects, in other words pretty light.
Fast forward about 2 months. Added weight, 400 gallons fuel and 200 gallons of water, in other words HEAVY.
I have changed oil, Delo 100 40w. Changed fuel filters, added vacuum gauges to RACOR filters, cleaned air sep main filters, but not vacuum breaker, replaced fuel priming pump (the one that looks like a 1 lb. coffee can)that didn't work and had no check valves inside, other pump works ok. The Racor filters were 2 micron and the spares were 2 micron as well so because of the black stringy stuff that showed in the view bowl I put 2 micron filters back to keep things clean and am keeping an eye on the restriction gauges, currently 5lbs port and 7lbs starboard, I will put 10 micron filters in next time until I am sure of the fuel condition.
No load, engines turn 2500 +-.
Yesterday, fishing trip return, engines would only turn about 1850 rpms.
After a couple hours watching the grey smoke we cooled down the engines and shut them off and went diving.
The bottom looked. as my professional diver buddy said "looked like a dock". The bottom was cleaned good 16 days ago, and my regular diver says the bottom growth, is just out of control.

My question is, do I have an engine problem, prop problem, growth problem or ?
All opinions welcomed.

Thanks guys,
30 microns and a clean bottom it is.
Thanks so much and I will report back soon.
Rob

The props were stamped 28 but didn't see the pitch because of fouling. There was some prop work but I can't find specs right now. will research more.
One other thing, Dual floscans, Starboard indicates much more fuel burn than Port. EX: Port 5 gph- Star 7.5 gph pretty even thru rpm range.
Diver works tomorrow, repeats the growth is crazy, never seen anything like, it the water is 78*
Rob

First I would like to thank everyone who has responded to my post.
After talking to my diver today he convinced me that even though now is not the best time to do bottom paint, it really needs bottom paint! It is clean for now but it will be overgrown in the next 10 days or so. I have a couple of things coming up but as soon as possible it is into the boatyard for bottom maintainence.
Now, as long as it is clean for the time being, I will change the Racors fron 2 micron to 30 micron, and give it a trial this weekend and see how she runs.
In answer to Capt J, about the condition of the secondary filter condition, I changed both of them when I changed toe Racors', should I change them again? About 10 hours since installing the Frams with 2 micron Racors ahead of them, about 140 gallons of fuel burned.
Ralph, no installed pressure gauge after the pump.
Ron, and all I will keep you all informed as we go along.
We will get this thing running right sooner or later.

Quick update on 6V92 Detriots, low rpms.
Per Info from you guys.
I pulled out the 2 micron Racor filters, the starboard filter was 3/4 discolored from ?, wasn't water as there was no water in sight bowl, and black fine strands of something, floating in filter fuel which I drained out to get the sediment out of the bowl, sediment in sightglass appeared to be, sand, dirt, debris of unknown origin.
Black algae like organisms globbed on the outside of the filter element, a real witches brew.
Cleaned out the mess and installed 2 new 30 micron elements.
I talked to my diver and showed him my appreciation for doing an extreme cleaning.
The engines sounded way happier, both settled into an even idle,(starboard had been idling at 670+-, port at 605+-) both now idle smoothly at 605 rpm.
No more grey smoke and without a lot of trim tab tuning both were turning about 2290 rpm.
Next step is to paint the bottom, and keep running the old fuel out and keep an eye on the filters.
Those are some good ol engines, I don't care what anyone says.

Thanks, all for all of your time working thru this.
Now, the watermaker needs some TLC.

Will do, Thanks

Here is a photo of a dirty filter.