I tested the HD, it's rate is significantly higher than what I am getting on Ethernet downstream, so that isn't the bottleneck.

I also noticed that when it hits its peak of ~540kbps downstream I start getting numerous collisions according to the transceiver. It's connected directly to my modem, which has an integrated 4-port switch in it. Being on a switch, connected directly to the modem, where would the collisions be coming from?