I too have the cisco 3825 and the past week have had horrible packet loss and latency. I called tech support and they said it might be a modem problem so I should take it in and exchange it. Well I own my modem so its not possible. The next day i tested the speeds at speedtest.net. My download speed was fine at 50+MB/s but my upload speed was 0.01MB/s. I called tech support again and they said its probably not a modem issue but a network issue and I should go to echat.rogers.com to ask them to run some test or something.
That was a few days ago. It seems a bit better now. I put my router in bridged mode and use an external router and maybe that has helped.
It would be interesting to hear if this is a problem related to the cisco modems and if so then something has changed on the network that hinders their function. If so I think they need to fix it or replace my expensive modem to one that is compatible.