I'd call Comcast and ask them to check their system, tell them you are having a slow connection to this particular server. They should be able to ping it, and see where the slow-down is happening.

We used to have Comcast, but every once in a while, we'd be able to reach other sites, but not our own server because of specific problems in their system. We'd have to drive to my old office, and upload the next day's pets from there, which was really annoying. We haven't had that happen even once since we switched to Verizon FiOS, thank goodness!