Low Gpu Usage at higher chunks

Heres a screenshot of my game and usage at 16 chunks http://puu.sh/eBPtB/bc81451720.jpg gpu usage is around 33% usually most times and when I turn the chunks to 32 the gpu usage goes down to 10% and the framerate drops 66% almost to scale with gpu usage http://puu.sh/eBPwH/a6c75e75ee.jpg