We are looking at toning the glass reflections. They are the thing washing the displays out.
Please try to increase "Control response" on the yaw axis to try and give yourself more fine-grained control near the center position. See what feels best.
Please watch the "Operating the Throttle" tutorial, this is explained in the tutorial. The tutorials can be accessed via Plugins > TBM900 > Tutorials.
Can you please describe a bit more about the circumstances when this happens? Mode AP modes were active, what controls have been actuated, etc. The aircraft should normally never descend on its own when it is in ALT-hold mode. The notable exception being Emergency Descent Mode when a cabin pressurization leak is detected. I assume you are not simulating cabin pressure loss. A screenshot in the moment would be perfect. This can be simply made via SHIFT+SPACE and the screenshots are saved under "Output" in the simulator. This should help shed light on the problems.