slow performance on after effects with fast pc.

You still don't tell us what effects you're applying and exactly what footage you're working with. Try updating your GPU drivers depending on the brand and model. After Effects gives you a suggestion to change the renderer, try right there changing to something other than "Software Only".

Your system specs are pretty good, but could you tell us what version of After Effects you're using, what footage you're working with, as many details as possible other than what effects you're applying or tools you're using, everything this is important to get a more general idea of the possible issue.