Sorry if this isn't the right sub for this.

I got a new Arris SB8200 when I upgraded to Cox Gigablast (940 down / 35 up) a few weeks ago. It seemed to work great hovering around 30 up, but this past week or so, my upload speeds have been running consistently less than 1 Mbps. Download speeds have stayed consistent.

However, on speedtest.net when connecting to my ISP in my city (Cox - Oklahoma City), I get much closer to my actual rated speeds. Connecting anywhere else seems to drop my upload speed to <1. It's so slow that file uploads are erroring out because it's taking too long.

Is this possibly a sign of a bad modem, or is Cox just screwing with me? I feel like it's just Cox given that it was working at the start. However, other people I know on Cox seem to have no problems. Support claims no problems on their end, did the whole troubleshoot routine, etc. and says it's probably my hardware and to try their modem. I really would rather use my own modem/router setup instead of their Panoramic Wifi modem router combo.

Thanks!

EDIT: I should add that I have tried on both laptops connected via wifi and my desktop connected via ethernet to the router. Same results either way, so I think I can rule out a faulty CAT6 cable or bad keystone stripping job. I even tried connecting directly to the modem too, so that should rule out the router.