Suzuki DF 150 engine rpm and trim problem

[PowerA]

Suzuki DF150, year 2011
Abt. 250 hours.

The whole bottom unit was changed after hitting an underwater rock in cruising speed.
Not sure how this can be related to the problem, but after the service the engines revs down about 300 rpm when I trim the engine down.
As soon as I let go of the button the rpm goes back up.
The speed and rpm go down immediately when I hit the trim button.
Nothing happens to the rpm when trimming up, that works just as it should.

Any ideas what could be the problem?

[Harper]

***! That's a strange one! My first reaction was a binding motor/pump in the trim/tilt system, bad enough to load the alternator, but that would effect it both directions, and I'm pretty sure that's not it anyway. So the only thing I can think of would be that you mucked up the tilt/trim when you hit that rock. Something got bent or broken in the rams or the endlinks, causing some binding as you lower it, again pulling more amps from the alternator. Still seems unreasonable to think that would change your RPMs though, without blowing a fuse or something.

But it's the only thought I can muster at the moment.

(Haha....I forgot that the program censors the word w-o-w, hence the *** at the beginning)