I recently moved to Chicago, and got RCN through my building. Ever since I moved in, I've had fluctuating (but consistently there) packetloss to a game server that is colocated about 15 miles away (colocrossing). I am actually unable to play on the server because of it.
This was not at all an issue with my previous ISP, and many other people are able to connect without significant/any packet loss. This packetloss also persists for me whether or not the server is empty.
According to the RCN speedtest, my speeds and signal levels are okay. However, ping -t shows ~3% packetloss to the server, and teamspeak shows 5% inbound packetloss and 0.5% outbound packetloss. This is quite variable, and 5% seems to be the peak, but it usually is around 0.25%-0.5%, and outbound packetloss seems to be more prevalent (although not in this instance).
Google has roughly ~1% packetloss, and various other servers also have appreciable packetloss. I've also run ping -t on various servers at the same time, and they almost always time out on a ping simultaneously.
As I've written this post, packetloss as measured by teamspeak has gone from 0.5% to 5% and back down to 0.4%. It's highly variable, but almost always there.
Please let me know if there's any other information I can provide, and thanks for any help you can provide.