Is it a sign that the brushes need replacing when the router speeds up and slows down on its own, without the dial moving of course, I have a dial lock installed on mine.
I had the one of the brushes act up on me once. The router starting sounding weird and slowed down to a crawl. When I took the brushes out to check one of them had a bend in the spring and wire. I bent it straight and the router has acted fine since.
So while I’m not an expert on electric motors, my experience says that it may be the brushes.