C7000-100NAS - 100 Mbs Download, 1 Mbs upload?

I have the C7000-100NAS as well and had simular results.

I fixed them but replacing exsiting cable with new RG6 cable and connectors rated to 1000MHz. and what helped the most improving upload speeds was using a 5-1005MHz spiltter with EMI shielding and wiring it to a proper earth ground if your cable drop isn't grounded when it comes into the house.

Try this

https://www.amazon.com/gp/product/B007YV0UQW/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

try hooking it up grounded and ungrounded and compare results.

It will also drop your power level down a bit which might not be a bad thing in your case.

Replace all splitters yearly or when performance slows! 

If all else fails have the cable company to install a new drop and have a line tech come out and adjust your neighboorhood cable power amps.