Summary

The pinned post on the forums here labeled "Internet Troubleshooting Tips" states you can view "Upstream Signal to Noise Ratio" and "Upstream Receive Power".

However I am not seeing such stats available for Xfinity's provided Cable Gateway XB8.

Expectation

I would expect a first-party device (XB8 in this case) to provide the best support, hence provide the most stats, including "Upstream Signal to Noise Ratio" and "Upstream Receive Power".

Technical Assumptions

I have never actually seen a cable modem/gateway provide Upstream SNR or Upstream Receive Power. By definition, these two stats can only be calculated at the ISP's end. However, such stats would be very helpful in debugging upload issues if they can be sent back to the modem/gateway and listed in it's stats page. The Transmit Upstream Power Level sometimes isn't enough to correlate upload packet loss issues.

Full details of the XB8 Modem