Spectrum is the second-largest cable ISP in the US, covering 41 states. Its plans are simple, three tiers, but real-world speeds depend on your local node and modem.
Bypass any router and test directly off the Spectrum modem. If wired-direct still fails, request a free modem swap (older DOCSIS 3.0 units cap at 400 Mbps in practice).
All Spectrum cable plans are asymmetric. The 35 Mbps upload on Gig is fine for one HD call but struggles with simultaneous uploads.
Usually a poor splitter or oxidised F-connector. Inspect the wall plate and the splitter in your basement; replace anything corroded.