Philly,
the 6X is an entry level computer radio. You are asking it to do more than it can handle. You're looking for the type of performance an 8U super or 9C can give you.

Please check out the travel of your two servos when moved as ailerons, I suspect you'll find you have differential travel there as well, as the 6X doesn't have the ability to adjust the 2 servo's flap movement separately.