I recently got a CM600 to replace the Arris modem I've always rented from Suddenlink. Once it was up and running it was working great for the first day or so, but since then I've had to restart it a minimum of once a day b/c my speeds were dropping from the 105-110mbps range down to 1-3mbps randomly. Every time I reset the modem my speeds jump back up to normal.

I tried only resetting my router several times, but with no change (Nighthawk X6S).

I've checked and can't find anything about an update I can apply and can't figure out what's going on. Just to get through for a while I set up the Arris I was renting and hadn't turned in yet, and it's been rock solid for 3 weeks straight.

I'd really like to get to my own modem, and read a ton of good things about the CM600, but don't know what might be wrong.

Thoughts/suggestions?

Look at your modem logs - 192.168.100.1
I had an issue with a CM400 that was either overheating, a design flaw, or some code issues. It basically would repeat these lines:

Time Not Established
Warning (5)
B-INIT-RNG Failure - Retries exceeded
Time Not Established
Critical (3)
No Ranging Response received - T3 time-out

Netgear support replaced no problem, but if this is from a retailer, you might be able to take it back and swap it out.

Interesting. I had those problems with a CM700, but that was a Puma chipset issue likely. I replaced it with a CM600 which has been rock solid.

Would be interested to see what error messages it does have in the logs above.

Does it have good air flow clearance? I do recall that it does run a bit hot too...

I also had an overheating issue with my CM400. I think I sent it back to Netgear or they updated the firmware and it fixed it. Can't remember. This was like 4 years ago. But I tested my hypothesis out by covering it with a blanket and seeing how long before my connection became shoddy. Then I put a fan blowing directly at it and measuring the time.

Thanks all, I'll set it back up and check logs once it slows down. I knew about the Puma chipset issue, which was why I went with the CM600, so was really at a loss when it started happening. I'm past the 30 day return window, so no matter what it looks like I'll be working with Netgear on a fix.