Perhaps it's the modem itself? I've noticed that with the Comcast switchover that certain Linksys modems(the version 1 cable modems) don't sync with the network anymore. The Version 2's work fine and my motorola surfboard 4200 seems to be a-ok. No downtime for at least a half a month since the last 2 hour downtime. Personally I'm opting for DSL, I'm only about 10K away from the CO anyways, I should be able to get a nice T1 line in.
Well darn it, they just suck then. I don't see what the problem could be. The Techs seemed to have tried everything they could, though admittedly that isn't much. The Tech that came over to replace my old modem was clueless as all hell, I need to get paid as much as he does. I know more damnit!
In fact in the 7 truck-rolls most of the pieces were replaced multiple times.