i don't know a whole lot, so take this with a grain of salt. you just put on a centerrest, and it's all the way against the riser. that could be your problem. i'm not familiar with the gamemaster, but i'm betting that if you move your rest to where it's centershot, instead of against the riser, you'll see a difference in the what the bow wants for an arrow. from my little bit of experience, the further past center shot the riser is at, the weaker spine that will be needed to get good flight. my 2 cents.
-rich