4k playback on Plex for Apple TV 4k

I have a Apple TV 4k, Windows 10 latest updates, icore7 6 core 8770k, 32gb ddr4 ram, 4gb GeForce 970 video card, Samsung 850 pro ssd drive, wired network, but cannot play 4k movies without being transcoded to a lower resolution.
The audio works perfect, I get truehd and atmos, the movies I’m trying to play are mis files. They play perfect on Plex in windows at full 4k resolution.
I’m kinda new to streaming my movies from my pc to the tv.
Any help will be greatly appreciated
Albert Rivera