Well, I can't start new threads so I posted in this thread, although it's related to version 2.3.

Meanwhile I used the repair option of the 727 installer. After this the Captain_Sim.p721.sys.gau file appeared in the panel folder. But the pitch function still didn't work. So I replaced that file with the file from the fix. Now the pitch function and altitude hold functions works. It's a little bit wobbly when disengaging altitude hold and adjusting the pitch, but all in all it finally works. I will do more testing tomorrow...

So thanks a lot again for your help :)

PS: I don't know why there was no Captain_Sim.p721.sys.gau file after the first installation. But I don't think it was due my anti virus software since I always add the entire FSX folder as an exception because of potential issues like this and to prevent lower frame rates.