CM1200 suffering massive bufferbloat issues when used with Comcast, who "supports this modem".

Current setup:

CM1200 ---> XR500 ---> Desktop computer (hard wired)

Scenario:

I recently moved out of my old place and into a new one, and my computer is now getting bufferbloat spikes of 255ms - 2000ms - causing me to have massive ping in games, voip, or even fail to upload files 1/3 of the time. The only thing I changed was my modem and location; Old modem was a CM1000. It's worth noting that my original location yielded perfect bufferbloat, and no changes have been made to the PC. PC is not the issue.

Things I've done:

Tech Visit, placed a filter on my line to up the upstream above normal noise. Not sure if it helped or not. Doubtful.
Called comcast an additional two times, and used their text based support. Text based support claims the modem is broken, meanwhile the 3 hour phone call support told me everything was fine and that I should contact netgear - signal str ect is great.
Tried plugging my pc directly into the modem, issue is aggravated.
Enabled QOS on my XR500, which mitigates some of the issue but it still spikes 250ms - 2000ms every 5 seconds.
Replaced my modem with an identical model. Issue persists, without any variation.
Replaced the coax cable twice, and the tech even replaced the fittings on the original cable. Currently using the comcast issued coax cable.

Modem Errors(x30 per day):

Dynamic range window violation
SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing

I suspect that this modem is not being configured correctly, either by comcast or netgear. I don't know enough to say for sure.

Forum Discussion

CM1200 Massive Bufferbloat