Well, disabling forces in P3D doesn't seem to be the fix...maybe it was using fsuipc for axis assignments, instead of assigning with P3D (I have all forces disabled in P3D). Just to cover all the bases, In fsforce profile manager, I would make sure you set trim function to be fsforce and NOT fsx in each of your fsforce profiles, and be sure you do the joystick test which is in the fsforce profile manager "Options" menu at the bottom (you may have to scroll down to find it).

The cool thing about fsforce trim function is that it works same as IRL, in that if you trim nose down, it moves the elevator centering force forward. The hardest part for me was finding a happy medium with "trim click amount" setting in options. I have finally settled on 30, but for some aircraft that is a bit too high, and for others a bit too low. Trim sensitivity is influenced by airspeed, so it's the slow aircraft for which 30 seems too low, and for fast aircraft it seems a bit high - shame it's not a profile option.

I have seen profiles on the FSForce site and I would venture to guess that you could write your own profile with its own trim function for each of your aircraft.