Can you keep an htop running by chance? It would be very helpful to see if CPU is maxxing out when the hitches happen, or if the swap file is growing, etc.
Any time it happens to me, it's usually low resources because of something. Most often some chrome tab (or 3) that are going crazy. I also discovered that one of the apps that I thought was using hardware acceleration actually wasn't. The CPU usage made it pretty clear that the CPU was doing a ton of work.
