Re: Unstable Internet
sounds almost exactly like my issue, but I have a XB6-T Technicolor modem and no router.
Asus Maximus VI Hero
Intel i7 4790k
Nvidia GTX 980
Gskill 1600 Mhz 4x4Gb
techs replaced my line with full fiber
all the coaxial copper in the apartment tests full speed, I have my own doodad that measures this and the technicians confirmed this too
performed exactly all of the OP troubleshooting steps, including a full (!) computer wipe (!) OS reset and still the same issue with the same symptoms!