@ thecreator
-Yes, we're both on the same ISP, MTS, and both on a DSL connection.
-Nope, one PC is hardly ever used, and mine is on about 12 hours a day, maybe once a week I'll leave it on overnight
-I haven't thought about phoning them to check anything for noise, but I'll put that on my list of things to do.
-It's a dynamic address
-Yes, I've set it to factory default multiple times. Last night I set it to factory defaults, and disabled different options like QoS, UPnP, everything that I knew wasn't needed. It ran for about 13 hours until it disconnected. I reset the modem and it connected again, and then about 4 minutes later it disconnected again.
-By network filtering, do you mean MAC Filtering? If so, no, that's disabled.
@bluenote
For the most part, I've had wireless disabled. I only re-enabled it for a bit to go online with my laptop, to see if the connection would still go down with my main PC unplugged from the network. I've disabled it since then, once again.
Tomorrow I'll go check my DI-604 at my friend's place (Set it up wrong so it wasn't going to work in the first place >_<) to see if it's disconnected. I'll also see if I can get someone to come here and test the line to see if there's any noise or interference, which will probably be next week since it's the weekend. Is there anything else you guys would suggest to try and make this more controlled? I'll go unplug every computer from the network except mine, turn off wireless, reset it to factory defaults and maybe re-flash to the 1.22b firmware, and then disable some of the options on it.
Edit: Connection's been up for 23 hours now

! Tonight I might connect the other PCs and see if it stays up. All I've done, like I said, unplugged other PCs and turned off wireless, reset to factory defaults, disabled things like UPnP, DNS Relay, Securespot, QoS, and set the WAN port speed to 100mbps instead of auto. Yesterday, when it disconnected after 13~ hours, I was streaming a couple of different videos. Today, I haven't torrented (in a few days), and I've kept downloading and streaming to a minimum, and it's been running fine. I do remember the last few times it disconnected I was downloading something, even if it was a small 10mb file on a site's FTP. Could this be pointing to the option that the router's getting overloaded with connections and it's somehow desyncing with the modem?