Another column to watch on the Processes tab is GDI Objects. A bad GDI leak can make your system crawl even though memory and CPU are normal.
You have to add the column (View / Set Columns / GDI Objects). I add it but leave most of the column out of site, then resize the column when I suspect a GDI leak.
Dave Plummer, the original author of Task Manager had a nice video about it and some secrets we didn’t know about it. He presented the video on Task Manager’s 30th anniversary (birthday?). His YouTube channel is Dave’s Garage.