I had the same issues, HEVC was stutterings insanely, was almost like i watched it in 5-10 fps.
I think i found out something, the PMP app you download from plex.tv’s website is not the real PMP somehow.
When i downloaded the correct release that you can find in the forums is like the old PMP player that you in fact installs, which you dont do with the other one.
After installing it my stuttering disappeared for all my HEVC materials.
Scroll down to the latest announcement and download the mac release, and see if its any better.
