FPS sags every 5-10 seconds.

What it looks like (the video contains the gameplay of GTA 5 and, for comparison, the gameplay of the witcher)
Before the appearance of drawdowns with hardware, I did nothing, programmatically too. Before recording, I scanned the system with ADW cleaner and antivirus. Overclocking the video card gave nothing.
In addition to GTA, FPS sags even in CS: GO (disabled multi-core processing and stopped sagging) and in DOTA2 (cured by accelerating the cooler on the video card).
The temperature of the iron is on the video, the temperature in the room is +27, outside is +35.
System: Processor - amd phenom II x6 1090T 3.4 Ghz Video card - gigabyte 750ti PSU - winard 650W OP - crucial 2x 4gb, win 8 x64 / Recently updated video card drivers.