Yes, your downstream power levels are too high. They should be somewhere in the range -6 to +10 dBmV. Though allow a bit for drift, so I'd want +9 max for a reliable connection.
You don't say whether you're testing your speeds via wired or wifi. Sounds like wifi?
Connect a computer direct to your hub via ethernet and post links to your speed tests from
http://www.thinkbroadband.com/speedtest.html and
http://www.speedtest.net/