You might try playing around with the nock point. If it's too low, particularly if you grip 3 under, it can result in erratic arrow flight. Run it up to 3/4", and see what happens to your arrow flight. You might not want to leave it there, but it's not going to hurt the bow to try it out. Generally speaking, if you run the nock point up too high, your arrows will impact too low, but they should fly well. If the nock point is too low, arrow flight will be erratic and you won't be able to group. If you don't see any improvement in your groups with the nock point higher, then drop it back down.