TLDR. CM3000 is solid.
Over the last 30 days with this modem, I tinkered around a lot with splitters, Ethernet over COAX, MOCA filters, and attenuators. Ultimately I settled on a simple design.
While tinkering, I was close to 1db on DS power levels, and 46db on US power levels using a 6db attenuator but I unequivocally observed uncorrectable packets using one. Upon removal, uncorrectables went back to zero. I could try a 3db attenuator but my wife got tired of me resetting the network.
Now power levels are around 7db DS and 40db US. I have a MOCA filter on the main line with an Amphenol 1675 2-way splitter, one side to the modem the other side is terminated with a cap. No cable boxes or COAX devices. My home’s in-wall COAX lines are also capped for weather protection.
Conclusion. This is a solid, Xfinity recommended modem. Sadly for CM2000 buyers, the CM3000 is more practical as it has mid-split as well as a 2.5gb port, in addition to the two 1gb ports which can also be used for LAG mode.
I love the simplicity and versatility. You can choose your configuration based on your service plan and devices. If you’re on a 1gb or lower plan or if your router doesn’t have a multi-gig port, LAG might help you with overall bandwidth to use any head room in your service or slightly reduce contention if you have a lot of devices running simultaneously at high utilization.
Since I’m on the 1.2gb service plan, and my RAX120 router has a 5gb port, I chose the single cable option to reach the maximum download speed and bandwidth. For me, on good days, I see speeds up to 1.4gb download. So, I have an expensive CAT 8 cable between the devices which defaults to the 2.5gb link speed. This is twice my service plan speed so I don’t see any contention even with my Ring devices constantly recording the neighbor’s cat.
For the last 7 days, I usually see one T3 error per day in the log, but system uptime is 7 days. Not sure if these T3s are actually causing resets. But the CM1200 had the same T3s as well. So definitely not a modem problem and our video conferences during the work day never disconnect.
One issue I have is with the speed tests on the 1.2gb/200mb Xfinity service. Upload is always 220-240mb but download is not consistent. Sometimes I see the full bandwidth of 1.4gb/240mb which includes the headroom. Sometimes I see 400mb down, or 850mb down but I suspect this is Xfinity throttling the service and not a modem problem. I saw a similar problem before buying this modem while using my CM1200 modem in LAG mode.
Finally, for anyone considering a higher upstream service of 200mb+. The mid-split capabilities on this modem really do help a lot compared to the previous 40mb speed. I wish Xfinity would use the higher DOCSIS 3.1 frequencies for better channel separation but they don’t. Either way the higher upstream speed helps a lot if you work from home, on conference calls and have those pesky Ring devices on.
Good luck.
