C32A cruising RPM

1800 to 1900 sounds sweet. What is your max loaded RPM?

If the engines turn the 2300 rated RPM, max cruise would be 2000 rpm

It depends on the boat... ours are on an 84 Lazzara Skylounge and even though they re showing 75 % at 2000 I rarely run them above 1900. That gives us a solid 24kts in smooth water on 51 GPH each and 60% load

This is not good.
Bottom and gear clean?

If your not making RPM, the engines could be overloaded. Even not by many RPMs, you could stand a bit over 2350 than under.

If everything is clean and the engines have been checked then you need to check the wheels and probably take a little pitch out

You need to take pitch out and engines should hit at least 2350 rpms with full fuel/water. A little more is even better. Boat getting heavier, more gear, bottom not as smooth due to many layers of bottom paint (bottom paint is heavy too, so add up the weight of every single layer), engines not making the same HP as they age, air temperature, water temperature, coolers not as efficient (aftercooler etc.) could all be reasons for the drop in RPMS.

I'm dealing with a brand new yacht right now that made RPM's at the factory where the water temp is between 60-70F and air temp was around 60F when sea trialed. Here in South Florida with air temp 90F and water temp in the 80's, it's shy on RPM and they're taking pitch out of the props.

Cruise RPM is 80% load and the RPM's will vary depending on how much weight you have in the boat. As you burn off fuel, load will drop a little at a given RPM.

Did the RPM ever come up where your at?
Have you moved on board? Moved clothes, tools, spares, mother in law and other heady items of dead weight?
Last fuel filter change?

C32 Acert specs to a 2300 RPM WOT, so your goal should be, say, 2310-2325. Double check the top end spec for your engines?

https://www.cat.com/en_US/products/...s/commercial-propulsion-engines/18499457.html

Like Ralph says, "Last fuel filter change?"
Eliminate any cheap (er) variables, first. Replace primary and secondary fuel filters and be sure of the type of filters. I was once involved with a brand-new Mikelson sportfisher that wouldn't come up to full RPM. The boat was in and out of the travelift several times with prop work and other professional headscratching. The problem turned out to be 2 micron Racors not passing enough fuel. Even having two manifolded 2 micron filters opened for each engine wasn't enough. Sorry, I don't remember the engines make or series.

That was a real dumb blunder as fuel pressure is one of the first things to check. As for the OP also see what your fuel pressure is, that should tell you exactly if you have any fuel restrictions, also look at boost at WOT. If WOT should be 2300, I like to see over that a bit with full fuel and water...….2325-2350.....