Slow speed, intermittent connection or no internet access occurs usually out of cable signal level, out of acceptable range and it will be resolved after the power level are adjusted by the service provider. So for this we need to check the cable signal level to confirm what causing this issue to proceed further.

http://arris.force.com/consumers/articles/General_FAQs/S33-Cable-Signal-Levels

May i know who is your internet service provider is and what is your current speed plan.

RCN, 400mbps

I would suggest checking the cable signal levels to make sure that all the signals are within range.

http://arris.force.com/consumers/articles/General_FAQs/S33-Cable-Signal-Levels

If the signals are not within range, I request that to contact your internet service provider and ask them to adjust the signals within range.