Spine could be the issue, but I also wonder if (I am assuming you nock under) since the Gamegetter is a thicker aluminum shaft then the Beaman ICS carbon, could you be getting a bounce off your shelf (do you shoot off your shelf?). If it looks like you are presenting with a "nock high" sort of wobble you might try nocking over briefly and seeing how it flys.
Or I could be totally wrong.