I do not know what is causing your issue. However, were it my system,
I would do the following:
Open task manager, and set to "always on top". Then I would run a game and see what my CPU utilization is at. If high then I would download and run HWmonitor and re-check CPU utilization and also temps, while playing one of the aforementioned games. Then report both figures back to this thread.
Install latest firmware for Gigabyte GA-B75-D3V, if not updated already:
https://www.gigabyte.com/Motherboard/GA-B75-D3V-rev-10#support-dl
Windows defender: I would fully update Windows 10, then temporarily disable Windows Defender or any anti-virus/trojan/malware software to see if it's the cause.
different ram brand / timing: Do you have one or two RAM sticks installed? If two, are they different brands and/or timings?
connectivity: Wired via Ethernet, or Wi-Fi? If Wi-Fi, is it using 5 GHz spectrum?
hdd fragmentation: If using a hard disk drive, and not SSD, for storage, I would administrative run: chkdsk /r from the command prompt. After that's completed I would download and run defraggler, to minimize any data fragmentation on the drive.
Question: Just out of curiosity, what is the brand and model of both your HDD and your power supply? This question is purely out of my own curiosity.