James, unplug both motors - plug it in and after it arms, slowly move the sticks - watch the swash carefully and see if it reacts properly. Should go up and down smoothly as you move the throttle and right, left, forward and back accordingly. In forward the front servo should go down as the rear two go up and the opposite in reverse. If all is going properly now move everything quickly and see if still works. I have a feeling you have a broken servo gear. Of course it might only slip under load, but it's worth a shot. Don't know if that would cause the shakes or not, but that's possible too.