2 suggestions...
Firstly is it definatly in relation to hull flying or is it speed?
The 5.2 had a weak pull down system on the rudder blades that caused the blade to move back when moving at high speed.
To check this lock down your blade and pull from the bottom to see how much play you get. It shouldn't move more than 1 cm if it does you might want to consider a 2:1 pull down system or some other method.

Secondly if it is hull flying causing the problem it could be a hull is out of alignment or a center board.