I picked up my BUSA Citabria Pro at an auction already built so I assumed the plane was straight and true, firewall included. Well I was wrong and the engine had 2 degrees of up thrust in it, a Robart incidence meter showed the error. After taking the time to shim the engine I flew the plane again and it flew MUCH better. Addition of quite a bit of aileron differential calmed it down in the turns and now it's a big teddy bear. On high wing "Cub" type planes like these it's critical to get all of the angles and control throws right.

I would try adding some down thrust to the engine and dail in some differntial into the ailerons. A good starting point would be to cut the downward throw by 25% and see how it flies.