Netgear CM1000 Slow Speeds

[imEMT]

A few months ago, I picked up a CM1000 to replace the Comcast provided gateway I have been having issues with. Everything has been working up until recently when I noticed that I cannot get more than ~80 download and ~5 upload. I am on the Xfinity Blast package which gives 500/15. Before the problem started occuring, I was able to consistently get ~450 download over WiFi, and now I can't.

For troubleshooting, I have tested multiple computers and phones. I plugged a laptop into my router (Nighthawk X6) via ethernet and still had the problem, so I went through my modem and the speeds were still low. I am pretty sure it is Comcast's fault due to nothing being changed hardware or software wise in the last 2 months, but I do not have another modem to test with before I contact Comcast. I can provide modem information needed, but I'm not the most intelligent with networking, so that's why I'm posting.

[FURRYe38]

Have the ISP check the signal and quality up to the modem.

Be sure there are no coax cable line splitters in between the mode  and ISP service box.

Speed test with a wired PC connected to the modem directly.