Your SNR/Attenuation should give you around 8128kbps or very close.
Have you plugged a phone in and listened for noise on the line.
You might want to try routerstats from http://www.vwlowen.co.uk/internet/files.htm
to give you a view of what happens overtime.
I would phone support if you are out of your 10 day training period - they should be able to see the connection history and check the line. Might be a faulty line card at the exchange.