I just noticed this out of the blue about 2 weeks ago. I have ~28 Mbit down and ~5 Mbit up normally, however recently upload has dropped to as low as 0.5 Mbit. Sometimes this is relfected on speedtest.net, sometimes it isn't. The only way I can really notice is if I am doing live streaming (games) to Twitch.tv or getting lag spikes in games (which have even caused me to disconnect a few times). My download speed is still perfect...zero issues with down speed.
I have a hunch that the problem is my old DOCSIS 2.0 modem (SB5100), but the EOL was back in July of 2013 and I have had absolutely zero issues with the modem and its speed until about 2 weeks ago. I have also heard that upgrading to DOCSIS 3.0 is only relevant if you are using much higher speeds.
I've seen a bunch of other posts stating similar issues, but they are usually both down and up speed. Is anyone else having upload problems ONLY? Or does anyone else have any idea on how to fix?