I first noticed this a little while ago (haven't been gaming much lately since my room is hot enough as is). My gpu is an XFX 280x. I haven't always had this problem and when I first noticed the low utilization, I was using 14.6 drivers. I thought that maybe updating to 14.7 would fix the problem, but no such luck. Perhaps going back to the LTR 14.4 would be the best course of action.
In games in the past, the gpu almost always maxes long before the cpu does.