Slow upload speeds after replacing modem.

EDIT: 2023/11/01

RESOLVED: Long story short, you MUST notify Comcast of the router swap - to get it properly provisioned. The Comcast gateway I was leasing was provisioned for both internet and phone/voip but since the CAX30 has no voip capabilities, the same provisioning could not be applied to it. After speaking with Comcast support on Reddit and making them aware that I'd be cancelling voip going forward, they applied the proper provisioning. The next day I was not only receiving 5x the upstream I was receiving before, but downstream had also increased. Thanks

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I purchased a Netgear Nighthawk CAX30 modem to replace the modem I lease from Xfinity. I pay for 800down/100up service - but am getting about 700/6 with the Nighthawk. I can live with the downstream, but 6Mbps upstream is a problem for a home full of students, telecommuters and videoconferencers 

For comparison, when I was using the Xfinity modem I was getting around 800 down and 50-60 up.

Is there any way Comcast can check that the modem was provisioned correctly? Or perhaps do some line tests?

These are some errors from the event log, but I'm not sure what they mean. Below that are "cable diagnostics"

• UCD invalid or channel unusable;CM-MAC=<MAC ADDRESS OMITTED>;CMTS-MAC=<MAC ADDRESS OMITTED>;CM-QOS=1.1;CM-VER=3.1;

• No Ranging Response received - T3 time-out;CM-MAC=<MAC ADDRESS OMITTED>;CMTS-MAC=<MAC ADDRESS OMITTED>;CM-QOS=1.1;CM-VER=3.1;

• SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;CM-MAC=<MAC ADDRESS OMITTED>;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;