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.
Gpu: 280x
Cpu: i5-4430
In games in the past, the gpu almost always maxes long before the cpu does.