I have major updating problems with steam for some reason. A lot of games will download updates for a second, then stop, then spike back to downloading, then stop. Patches can take *DAYS* to finish. Tried completely wiping out and reinstalling steam multiple times, changing download servers, no dice. Occasionally forcing an error check on the game will correct it, maybe one in 10 attempts. It's persisted through multiple formats/reinstalls of Windows as well.
The odd part is the core game downloads are always fine, its strictly game updates that do this. It doesn't seem to be a network thing either, it's persisted through a complete move to a new town, with a brand new router/switch/etc and a totally different ISP.