Couple of years ago, much the same security setup as you. Avast! a/v free, COMODO firewall free. I gave up on COMODO as I was running the system (see sigs below) below and it would actually freeze/hang for several seconds whenever off-line or when installing new software; also even when online. D + was the culprit, and the automatic checking to the cloud always took some time to complete. Once COMODO was removed, (and D + along with it) lagging/hang/freeze was no more. Solution was to use another HIPS capable firewall such as Online Armor.

Running D + just got to be too much, so COMODO went out the door. Running COMODO without D + was not an option, otherwise what was the point?

I suspect that on some older machines it just does not work as well as it should, even if the machine exceeds minimum requirements as this one does.