Gpu usage amd and fps drop

Hi, i monitor my pc with mai afterburner and in all games i play my gpu usage is 99% but random goes down to 20-30 % and drop also the fps.

Video card hd7750 sapphire , fx8350 , mobo asrock 970 extreme4, psu aurum600gold.

All temps are fine , what can cause this gpu usage drop? What program can i run for more details ?
imgur.com/jUxIHPh

Clean your computer externally and internally by checking for malware.