What am I doing wrong when previewing on my new beefy PC?

[zancoisrice]

I just purchased a beefy new PC and I'm still having playback lag and slow speeds when previewing. 

PC Specs:

AMD Threadripper Ryzen 3990x (64 Core)

128GB Ram

1TB M.2 SSD

GTX 980 TI (Will replace with 3000 series when launched)

1200Watt power supply.

I cannot figure out why my machine is running so slow when previewing 50% 1080 video
My video footage is running off the M.2 drive. I cannot understand this. I watch Linus on tech run multiple 4k videos at once without performance issue however its the opposite on my computer. What am I doing wrong?

Please help.