It's probably a Comcast problem. I'm having similar speed issues, only both upload and download speeds are affected. After calling up to ask why my speeds hadn't been upgraded from 8 Mbps to 12 Mbps, they actually dropped to around 6 Mbps. Technician came out... did all of the usual stuff... no joy. He even swapped out my modem with one of their new DOCSIS 3 modems... no difference. He left without fixing the problem, saying that he would submit a line ticket. I'm guessing that it's related to the speed upgrade they did, and that some of us are going to get screwed for a while.