there are people literally maxing out their TW connections. I doubt you're being dropped off the network because of that.
Besides, is the TW service not unmetered? AFAIK it's something they've boasted.
Sounds like the same problem i'm having with my NTL connection. I've had a swap for a new modem, then a new psu for the modem, and they've checked the signal level and cabling and can't find anything wrong with it.
I hope your problem is one of the above, as they're all easy to find. It's spooky intermittent stuff like i have that you don't want.