I'm having the same issues. I've done the reboot/unplug of the cable modem and my wifi router and still awful perfomance. I'm paying for 300mbps downloads and the speed test consistantly shows less than 5-10 mbps all the time. This started a couple of days ago. Normally it would be intermittment and then go away after a few hours, but now its just plain annoying. My next step is to connect my windows pc directly to the cable modem via lan coonection to see if I can verify that the performance comming into my cable modem is the issue. My cable modem is compatible based on xfinity's specs its a ARRIS SB6190.