Haven't had any trim problems so far.
I can only think of some guys using an acceleration setting in the FSX options which therefor repeats the command very fast or they have some custom FSUIPC or whatever (Joystick software for example) settings which interfere with the original trim response on this bird.

I'm using the standard key command of FSX, bound to joystick buttons. No big acceleration set and no custom settings at FSUIPC configured and she trims just fine.

What's your setup then?