R9 390 GPU barely being used?

Hey guys, so I have an R9 390 GPU and it's my understanding that it should be able to handle 4k video just fine. My only problem that I'm seeing though is that it's barely being used. When I bring up my AMD performance monitor I see that it will spike in usage every so often but even then it'll only spike to about 10% usage and then go back down to 0%. I do have GPU acceleration on and am using MadVR but it seems to mostly make use of my Intel CPU, having it using 80-100% of that and really only if I set it to 44FPS, lowest performance and no artifact masking. It kind of makes the software unusable for 4k unfortunately. 1080p and below, all works well and I can run stuff up to 144fps.

Do I just have to bite the bullet and update the rest of my hardware? This is what I have at the moment:

Intel I7-6700K 4.00 GHz
16GB RAM
AMD R9 390 GPU