Dropping internet access and losing upstream bonded channels - Time Warner Internet

As others have described, since the upgrade to 200/20 Mbps plan and DOCSIS 3.0 I am experiencing regular connection problems. Upstream bonded channels drop to 1 with power typically 54-57 dBmv. I use the Motorola MB7420 modem. Recycling modem power corrects the problem, giving 4 bonded upstream channels at 43-44 dBmv, then it typically reverts to one channel and high power after 1-2 hours. This happens many times throughout the day.

I only use TWC for internet access, not for television. The modem is connected directly to the coax input line that runs directly from the junction box on the outside of the house, there are no splitters or other junctions in between.

I appreciate any assistance and feedback on this.