Hi there,
I'm experiencing this too, but with horrible packet loss tacked on top. If you have a chance to look at other posts in this forum, it seems like many others are as well. Cox has been posting generic troubleshooting tips (restart modem, check lines, etc) to "remedy" this, then locking the forum topic. None of these generic steps work to fix your issue and it just seems like they are doing damage control for anyone who brings this up.
here's a reddit post going into detail about this:
https://www.reddit.com/r/CoxCommunications/comments/ftsai5/cox_has_widespread_congestion_on_the_upstream/
I've filed an FCC complaint towards Cox about this issue and hope that Cox will put some effort into expanding their infrastructure.