If you haven't misstated your "Up and Down" figures, then i think Montaque has the right idea.

Looking at how the torque rods are setup, you should get more down than up on BOTH ailerons. In other words, 3/4 down on the left and 5/8 up on the right, OR 3/4 down on the right and 5/8 up on the left.

But you claim that you are getting ) 5/8 up 3/4 down on the left and 3/4 up 5/8 down on the right. The only way this is possible is if the servo is moving more in one direction than the other.

What Tx are you using?