I had a 5 year old Linksys cable modem. When I was at home, after work, I got full speed no problem. But my brother always said that during the day it would stall out for 5-6 minutes at a time. I figured, what the hell, my modem is old, doesn't support DOCSIS 3.0, so the cable company won't touch it, and doesn't support higher speed connections. I purchased a new Motorola that supports 3.0.
I spent one night after work configuring it and getting it to work. Tested it out and got about 9mbps, not bad since I was paying for 12mbps. But then, it kept dropping every day. 7mbps the second day, 5mbps the third day, 3mbps the following afternoon. Checked out all the single strengths/noise ratio, all the statistics that the modem reported, everything good. Restarted the router once, no change. Called the cable company to ask about it, they checked everything out (remotely) said it seemed fine. They checked area usage and said there was no users with high usage that would cause it.
So today, I just checked my routers firmware, updated it, and suddenly it's back up to 18-19mbps. I can't tell if it's the firmware upgrade on my router that fixed it or not. Since it had been restarted since...