I have the same issue but the issue for me is concentrated in the evening hours. During the day speeds are absolutely fine, I can download at 5 MB/s (roughly 50 Mbps) but in the evening, that's when speeds go down.
I'm in contact with Time Warner now. They want to have a technician look at things even though I've told them that the issue is primarily an issue at night and not during the day. They did check the node utilization on the phone during the call and the Signature Home Tech (Tier-3 Support) didn't see anything wrong with the node so I figure that the issue is probably more than likely something further from the home.
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