4k playback on my new samsung 65"

Hi, just got my self a new samsung 65" 4k tv (UE65KS7005XXE) and wanted of course to playback a 4k movie. Trying to playback the file Star.Trek.Beyond.2016.UltraHD.BluRay.2160p.HEVC.BT2020.TrueHD 7.1.Atmos from my newly setup of plex server on freenas corral in a docker image. I5 with 32 gb memory. up to 4 cores and 32 gb is allocated to the docker running.
When streaming i see that the network is on about 25mb/s, cpu core 1 is showing 70% in use, the transcode area is on its own ssd, the movie is on WD nas discs.
The problem is that i get a lot of buffering. it says in the plex server that its transcoding audio truehd to eac3, video: direct stream, and a message transcoding (throttled)
Since this is my first setup i have no clue what so ever where of if i have done anything wrong. anyone have a helping hand? tnx