AP alt hold and trim

[Tobus 0]

Hi,

just bought the Short 360 and love it, but ... for some reason the trim reacts really sluggish in autopilot alt hold.

I fly her to desired altitude, set for cruise and trim, then set AP on ALT. It keeps alt but starts to gyrate in elevation pretty quickly. It seems due to very slow responding of the trim to the AP, thus it starts "chasing its own tail" by ever increasing values, eventually to -20 and +15 deg of trim. Eventually it goes into overspeeds and stalls. When trimming in manual the trimwheel goes much faster than on AP. Any pointers on solving this?