As far as I know, Spectrum, even the cable box, tops out at 720p or 1080i tops.. no 1080p.
I could be wrong.
As far as poor streaming quality, if try changing wifi channels.
Very weird.. and you've rebooted all of your network equipment? Are you using any special DNS settings on your router? You could try Google Public DNS settings on your router as an experiment, and if you like it, leave it set that way (22.214.171.124 and 126.96.36.199 are the addresses).