My first thought would be that you are moving the pin the wrong direction. Sounds simple, but it's an easy thing to do. But you stated your pin is at the top of the aperture, so I assume you have been moving it up. Check your nock point to make sure it hasn't slipped. Check the tiller and the timing. And, as buckeye said, make sure the A to A is in spec. Sounds to me like every time you shoot, something is moving.