Hi Jin,
I came to this forum looking for a problem like this. I am in Oceanside, have the 500/10 plan, and I am recently noticing massive slowdown to upload any decent size file (100MB+) to any number of places. I just started noticing it Friday March 18, but it could have started sooner. How slow? Well, Friday I was getting around 1.8 Mbps, but today less than 300 kbps. Like you, the speed tests look fine, and I even tried selecting servers outside of COX. It totally smells like a route problem, but I have tested uploads to Amazon S3, GitHub, YouTube. Google Drive, and Microsoft OneDrive. All behave in a similar manner., which is very strange and suspicious. If there is a route problem then I believe it is specific to COX. I have only been using COX for 11 months, and previously used Comcast in the SF Bay Area without this problem.
P.S. I have never exceeded my 1.2 TB data limit and currently have used 46% in the current cycle which ends in a few days.
