Cable modem reboots every 5 minutes

Newsreader? Here I was afraid we were a dying breed. 

Seriously, though, your signal levels are all over the board for as far back as I can see. Whether that's a modem issue or a line issue, I couldn't say for certain from here. Shutting down under load can be a sign of a bad modem, and getting a DOCSIS 3.0 modem wouldn't hurt anyway, but one of your DVRs is also a non-responder, which makes it more likely a signal issue.

I'd recommend checking any cable splitters or couplers you have access to in order to make sure nothing is loose or damaged. If there's any cable splitter near the modem that can be bypassed, at least for testing purposes, you may try that to see if the connection stabilizes, in which case the splitter may have gone bad. But if you've already checked those connections or if none of that improves it, then it's probably time for a service call.

I had the line replaced not too long ago, and everything's been fine since then. I purchased this modem about 2 years ago, and it's been fine up until now. I have no problems with surfing or streaming, although my computer has been kind of slow loading pages with lots of pictures and media sometimes. I thought it was a problem with my computer. If I'm getting up to 20 mbps on downloads (when the modem is working), shouldn't that mean that my line is probably good?

As Kip said the signals being reported by the modem are horribly out of specification and could be intermittently causing issues for you.  It would probably be best to arrange for a service call to determine if that is a signal or modem issue and correct it.  If there are still issues after that we can go from there.

As a matter of fact, I had to turn off my DVR and back on again to get it to work. What should my signal levels be at? I guess if I'm not getting the proper levels then it must be the line. I went to look at it and it's sitting on top of my neighbor's huge storage shed. It may be rubbing against it like it was rubbing against his house last time. This is sickening.

It could be that or even something inside or the modem itself.  For 3.0 modems, downstream levels should be -10 to +10 on all channels, all channels should be +/- 2db withing each other per tuner, upstream levels 35-52db, SNR +35db.

I got up on the ladder yesterday to check the cable and it's perfect. I just had it replaced a few years ago and it;s still in excellent shape, so I'm guessing that it's probably the modem. It's either that or Cox is limiting me to under 20 mBps and the connection is closed until the modem resets. It seems like I'm getting slower speeds now. too I don't know anymore.

For some reason I though you had a 3.0 modem already.  It might be worth trying an upgrade if it has been something you've been considering already.  One immediate benefit would be more consistent speeds even in situations where Internet demand is high.  The channel bonding feature of the 3.0 modems would balance that out better.

Here's another log file from tonight. Are these power levels okay?

Those power levels are not very good at all.  The signal to noise ratio should be a minimum 35db and -15 to +15 is considered acceptable receive power level however the closer to 0 the better.

But you still can't tell whether it's the modem or the line? If necessary I'll have to call Cox. I dread having to do that because it's a total hassle to meet these guys at a convenient time AND have them actually know what's wrong and fix it. The last time I had a problem it too 4 separate appointments and 4 different guys to finally work it out.

It really shouldn't take that many appointments to straighten something like this out. I'm sorry if you ever had an experience like that before. It could still be anywhere from the modem itself all the way out to the tap, but we should be able to figure it out in one shot.

Change out splitters. If you have say a 4 way that divides the signal out from the drop. I would suggest putting a good 2-way off the drop line then put the modem coax line on one side and then the 4 way splitter for the tv's on the other side.

Ive done so much reading the last few day trying to get the most out of my modem and read some stuff that i would have never thought of. Say a 4 way splitter drops the signal down 7.83 db then if you split that again with say a 2 way splitter that a 3.28 db loss of signal so right there you have over a 10 db loss in signal

I tried everything to make my DOCSIS 2.0 gateway to work. Cox here in Omaha no longer supports 2.0 anymore. There is a list of supported hardware on the website. I purchased a Netgear CG3000 DOCSIS 3.0 gateway and the problem with signal levels and being booted-off evaporated . . . 

It's good to hear replacing the device corrected the issue.  I suspect that the RF tuner in your previous device may be experiencing a problem if your symtpoms appeared to be signal related.

I was having similar problems. Do you have a DOCSIS 2.0 modem? If so, upgrade to a 3.0 modem or gateway. 2.0 is not supported by Cox in New Orleans. I just got the Cisco DPC3825 gateway (the only one offered) and it works fine. The set up instructions were WAY more complicated than they had to be, tho. Simply add your devices MAC addresses, then use the password to connect each device. My download speeds have increased dramatically and I've had no drops. Good luck!