That.
So first few basics.
This is always the most reliable way but it is the user friendly way. If you hit ctrl+alt+delete and look under memory, what speed is is showing your RAM at? Is it at 4000mhz?
What are your temperatures like? Use HWInfo (free version will work) to see what your CPU temps are.
Next, for your GPU, there are the power cables that go in the side. Did you use separate cables for each connector? In other words, the cables usually have two plugs on them. The main plug and a "pig tail" plug. Some will say it's fine, I am of the notion you should never use the pigtail. Always a separate cable for each plug.
Those are some initial thoughts and things to check.