I just installed a MacOS high Sierra guest on a MacOS high Sierra host on Parallels 13. Parallels tools in place and everything works. The host is a Mac Pro with 6 cores and 16Gb RAM. But why is the guest so slow? I've tried everything. I checked all processe in both host and guest, nothing strange, I assigned unlimited resources, 4 processors, 8Gb RAM and rebooted but it changes nothing. Watching a movie (a locally stored avi file) is very painful but only 34% guest CPU is used. I resently had an Ubuntu guest in Parallels 12 and it was fine. What more can I do? If it can't be faster Parallels is no use and I'd like my money back. However, it has worked in earlier releases.