I've been dealing with this exact same issue for months which coincidently enough began after upgrading service to Xfinity's Gigabit plan.. I also have the same modem as you, the Netgear CM700 and have never been able to achieve upload speeds above 6 Mbps on the Gigabit plan. The upload speeds on the Gigabit plan are advertised for up to 35 Mbps.
Just like teohenwhy and many other customers have mentioned, receiving upload speeds of 18 Mbps+ are absolutely 100% possible with this modem. However, as soon as you upgrade your service to the Gigabit plan the upload speeds are limited to 6 Mbps... I've called support, had techs visit and everything has always checked out as working normally.
So the question needs to be asked...
Why does the upload speed work as advertised and with faster speeds when using the same hardware (modem) on lower-tier plans such as Blast! Pro & Extreme Pro but after upgrading services to the Gigabit plan become provisioned to 6 Mbps?
Why are upload speeds intentionally being provisioned for slower speeds to customers who still have a DOCSIS 3.0 modem after switching to Xfinity's Gigabit plan?
Is there a proper configuration/boot file for our modem? I really hope this is not caused by an inadequate config/boot file being sent out to customers who still have DOCSIS 3.0 modems.
Any suggestions, insight or advice would be greatly appreciated. Thank you!
You can't get the Gigabit speed tier download or upload speeds with that modem. A DOCSIS 3.0 will revert to using a lower speed tier configuration file for both the download and the upload speeds if a Gigabit speed tier config file is attempted to be pushed to it. That would typically be the Performance speed tier config file.
I am facing a very similar situation. With the previous bootfile, my speeds were fine. Is there a way to revert back to the previous configuration until I can upgrade to a new modem? Being locked to 6 Mbps upload is rather unfortunate.