I just went back and read your post again...
If I read you right??? "Flies horrendously...constantly pitches up...tiring...checked and adjusted trim to exhaustion"
All that means to says to me is the trim force is all that's making it fly horrendously. I don't think you are saying vibration or shaking is your problem, right?
The Brantly trim system as you know, is simply an ARTIFICIAL force created by a stretched spring under the seat. Adjusting the pitch trim in a way that is NOT ARTIFICIAL involves pilot/passenger weights, fuel on board, aircraft empty CG, and if you have a way to add weight to the tail or in a pilot seat to NATURALLY adjust takeoff CG.
If the maintenance folks did anything to change the CG (I doubt it), that could cause your fore/aft trim issue. If lateral trim is your issue, they could have loosened the lateral trim spring that is just aft of the firewall and connects the left and right push/pull tubes????