FurMark 1.20.1.0

[Timeless]

I have a EVGA GTX 1070 SC GAMING ACX and when I am using FurMark sometimes the power of the GPU falls to 60-50% TDP for a second. Is that normal?
When I am playing DeadbyDaylight (an online game) sometimes the game will freeze and the GPU usage, power and CPU usage will fall. I wonder if that means my PSU is faulty.
Also I recently changed my motherboard, cpu and ram and the problem existed before.

[JeGX]

What is the model of your PSU (brand, power)?

[Timeless]

XFX PRO Black edition 850W XPS-850W-BEF. It's a good psu and I think my PC uses half of it.

Before upgrade
CPU: I7 4790K
Ram: 2x8 gb DDR3
ASUS B85 TUF vanguard

After upgrade:
CPU: I5 8600
Ram: 2x8 gb DDR4
ASUS H370 PLUS PRIME

[JeGX]

Could you do a 3 to 5 min stress-test with FurMark in 1024x768 and post the screenshot, I'd like to see the shape of the temperature graph?  What is the power target setting? 100 % TDP? If so try to set it to the max value (something like 120% or more). You can update this value using EVGA Precision  or MSI Afterburner.

[Timeless]

I tested it with TDP set at 112% (the maximum value Afterburner allowed) Dynamic background,  Burn-in, Xtreme burn-in, Post-FX and 8X MSAA.
At the 7min mark the temperature was 69º C.
https://ibb.co/bXmCUp

[JeGX]

Looks good (the temperature is not capped). Try to run your games with this power target setting, maybe that will improve the stability.