Is it a new chain? I couldn't tell from your post.
New chains definitely stretch a bit, at least in my experience with cheap ones.
Maybe the chain and cogs also had to "break into each other" slightly, the burrs and such. Either way, the chain probably sits better, now. Tighten up the chain again and ride it for a few more days.
Last edited by ryan_c; 12-07-04 at 05:49 PM.