Ocean 40 prop pitch

What RPM were you turning for 25 (KTS or MPH) @ WOT?
What RPM are you turning now? Really the same boat and weight @ WOT?
Why were your injectors adjusted?
Turn your syncro off. Both engines suffering?

Your ships bottom baby's-ass smooth? Your props have not been damaged? If you are spinning the same RPM and lost speed, then you forgot to throw the mother in law overboard with her junk.

If you are really not making the same WOT RPM as before, after ditching all the weight with clean bottom, remember ruel #13;
The rack on a 3126 takes special Cat tools. There is a rather large inventory just to make up this complete special tool kit.
Missing one of these tools for your higher (than trucks) HP ratings could have de-tuned your motor.
Rule #13, truck techs can't touch marine engines.

Oh, Loosing diameter will reduce speed also.
After grinding on props a few times for previous repairs, diameter is lost. No mater what the numbers on the hub say.

Prop scanned lately? Reports from previous owner?

Mostly correct.

As Capt Ralph mentioned, this is mostly correct. If your engines somehow got detuned or were loosing appreciable horsepower you would not be able to turn the same props at the same RPM. However, your speed can be affected by current and wind as others suggested. You can also be loosing speed due to inoperable trim tabs. How did you run previously to get 25 knots? Were you full tab down? Are you certain your tabs are working? The trim tabs lift the stern so if they are not working you can lose a lot of speed.

Let us know your results when you run with your trim tabs down. You will want to play around with them. Some boats, like mine, want every bit of tab down I have. Others like some % between up and down. If you can find some smooth water and play with them while watching your speed you can get a good sense of how your boat reacts to the tabs.

Also, forgot to mention, unless you have indicators telling you your tab position (doubtful) you will want to get a good idea of how long your tabs take to go from full up to full down and vice versa. You can simply do a mental time count as you cycle them back and forth. Mine are about 10-12 seconds to cycle full. Yours will be different I'm sure.