You might have to take some splits out, or see if you can get a signal amplifier. I had the same problem when I was living in my four-flat house in Dearborn: There were so many splitters in the box where the cable came into the house that the signal was too weak to support my Internet connection. The tech was kind enough to run a separate line for every flat from the pole, removing all of the splitters. The connection was outstanding after that.

I know that's not your situation, but all the splits are probably the problem.