Some software that can cause slowness may not be obvious. A common cause is a a single regular app that has "gone rogue" and is using too many system resources. The checks you used will not show that.
One of our fellow contributors here developed a free diagnostic app with which we can better help diagnose issues in a venue where we can neither see nor touch the poster's computer. It excels at identifying runaway or rogue processes.
It is safe, secure and will not reveal any personal or security information. EtreCheck is in the Mac App Store here: https://itunes.apple.com/us/app/etrecheck/id1423715984?mt=12 The free version should suffice.
I recommend going to the EtreCheck Help menu and looking under "More Help" for instructions in how to enable Full Disk Access. This will allow Etrecheck to work with a system change that happens in Mojave to see runaway apps.
>How to post the EtreCheck report:
Run Etrechcek, select “Report" from the left-hand pane (scroll down to the bottom of that pane to find):
When its report displays, click the "Share Report" icon from EtreCheck’s toolbar and then "Copy report” from the resulting dropdown.
⚠️ Please DO NOT highlight the text in the report before using Etrecheck’s “Copy report” command—that will garble the formatting and make the report slower and harder to evaluate.
NOTE: Changes in late 2018 to the forum software require you use the “Additional Text" icon (see example below) to embed the report into a post:
Paste the report into the resulting “Additional Text” window:
