Snail-paced Upload speeds on Xbox One X and Xfinity

Snail-paced Upload speeds on Xbox One X and Xfinity
Hi,

I recently updated my modem to the latest version available by Comcast. Around the same time, I got the latest Xbox One software update. Now, it seems that I am experiencing ~2Mbps uploads on both of my One X systems, though none of my other connected
devices are showing any signs of network traffic issues.

I've already spoken with Xfinity support at great lengths over the weekend with no resolution found on their end. Each device I tested had shown ~80% download speed capacity and over 100% upload speed capability (mobile phone, laptop, and desktop devices
tested). The Xboxes were ~60-70% download and ~3-5% upload speed.

This doesn't affect any streaming services (since they use minimal upload), but online gaming has been a nightmare because of this. Has anyone else experienced this recently, or anyone have any suggestions? I don't think it's my ISP at this point since
everything else works as expected.

Thanks in advance!

:)