Just as an update... the tech came out today and said it sounded like the bandwidth on our node was maxed. He said that during peak hours if there wasn't enough bandwidth we'd get randomly kicked. Likewise, if it wasn't peak hours and someone was using a ton of bandwidth (or several someones), then we could just as easily get disconnected. He said he was going to speak with his lead tech and work on it. Does this sound feasible?
I'm far from an expert but there are specific slots reserved for ranging and its seems unlikely to me that you would get T3 timeouts due to one user doing large downloads. The normal explanation I have heard for T3 time outs is Noise, normally on the upstream.
This is the Cisco page that explains error messages