ifdg/pss merge

Hi all!
I want to merge the ifdg A3xx series with the pss panel, I have read every merge method I found but always I have the same problem.
Fist the opt climb rate is very slow, it seems like the engines don' t have enough power. But the serius problem is the following:
After about 20 minutes of flying, the altitude indicator saws that the plane is turning left, but the plane is turning right a bit. The indicator then indicates a grater left turn, but the plane turns a bit right at the same rate as before. And then, suddenly the plane makes a very steep right turn ( 90 degrees bank angle) and starts to stall. There is nothing it can be done there to save the situation, the only I can do is to deactivate the autopilot, with no chance to be reactivated later sucessfuly.
I also have problem on the ils aproach, the plane starts to accelerate without stop 5nm before the runway when autopilot is on.
So , I can' t fly any ifdg with the pss panel. I would be really grateful if someone can help me find a solution to this problem.

Regards,
Ifikratis