Tom, have you installed the nVidia binary drivers? By default Redhat will use the open source "nv" driver, which I have found causes speed problems. Using the nVidia official drivers gave significant speedups for me, I highly recommend them.
You can find instructions for doing this here:
Unfortunately it's more complex than it otherwise would be as nVidia have not released Redhat 8 RPMs, so while you're at it you could email them and ask for psyche specific rpms.