Thanks for all your suggestions. I did fly the plane today with much less throws and still experienced the same differential effect, just flips to her right on squares and tight loops. The wings aren't stalling as there was enough entry speed. I found that one of the elev servos on it's max travel fluttered a bit (much like a backlash), could be the extreme end of the linkage. Replaced the servo and the new one did the same. But then, so far never flown the aircraft anywhere close to that range. I wonder if it still could be playing a part at low throws?
I am not very apprehensive about putting in time for doing the pull pull setup for the elevator (with a single servo only), only I would like to know if that would take care of the problem.
ALso, the model is balanced both ways and the throws have been re-checked for trueness through their travel.