Comcast XFINITY → Re: [Speed] What did Comcast do to my modem?

Truck roll time.

Probably a bad drop or a plant issue.

I've already stated TWICE that the rental modem was 100% fine for 6 months. The only variable that changed is the modem and it's power adapter. Everything else is identical. Due to when it happened, right after I put a move request in, it seems that Comcast did something to my modem. Also, at the beginning of that, they came out, and tested the levels, and everything was excellent.

Also, with a few exceptions, it's an all-or-nothing thing. It's either doing ~60mbps or ~.5mbps.

Then it sounds like they're not pushing the correct config file to your modem. Maybe you need to call and ask to speak to tier 2 tech support or even advanced tech support. It sounds like you are getting the runaround from the tier one tech support.

Maybe the new house that you moved into has some electrical issues. When was it built. Maybe you could post in the DSLR home improvement forum. Electrical issues can cause Cable TV/computer equipment to act up. My old house in Iowa built in 1949 had electrical issues that caused the TV to feed current into the cable line and almost fried a cable box. I had to go back to analog expanded basic. My current house is built in 1988 and has modern wiring and I have zero grounding issues whatsoever.

They've re-provisioned it about a dozen times, and it sometimes gets 60mbps... how would it work correctly sometimes without the correct config file?

This house was built in 1999, and it's possible it has issues, but that wouldn't explain why the other modem was rock solid for 6 months of heavy use (300-600GB/mo), in two different locations in the house (I had to move the router/modem for wireless signal reasons).

I'm pretty baffled, as I don't know what they can do to a modem other than mess up the provisioning, which they've already re-done a whole bunch of times. What's even weirder is that I'm now getting some middle-ground results in the 25-40mbps range, which I've only seen a couple of times before.

As someone else said, the modem could be going bad.

Also when you swapped modems you had to mess with the cables, have you reseated all connections? Something as simple as disconnecting and reconnecting every connection you can find between the modem and the drop can help with bad signal levels. Also how many splitters between the drop and the modem, if you have more than one redo the wiring so there is only one.

Also like others have said, your upstream power is way too high, got to get that down under 50 if you want a stable connection since it wanders a bit during the day. Are you seeing a lot of reboots of the modem? Check the log. If I saw 51db upstream on my modem I know it's going to hit 52 soon and reboot.

As I said before, I had tested with this modem many, many times, and all I did when swapping them recently was unplug one and plug the other one in.