Sounds to me like your memory or more likely CPU are getting more work than they can handle.
It's definitely only the editor -- game runs great - instant tooltips, rendering looks great, no lag or choppiness at all.
It "seems" like memory/CPU, but monitoring both and while in editor, CPU was barely hitting 18-20% usage, and memory was barely hitting 50% out of 16G.
...and of course, NOW, after restarting it again for about the 8th time -- now it seems fine.
tooltips are popping, rendering is instant. Very odd.
Seems like there was something stealing cpu cycles in the background that's now gone.