Sara,

I'd definitely ask your LBS about trim. I'm still getting the hang of it myself... I posted a thread here a few weeks back because I thought my front derailler was out of whack since I got chain rub up front when I was in the smaller cogs (higher speeds) in the back.

Turned out I wasn't using trim properly. On my bike, when I'm in those gears in back, my shifter for the front has a sort of half shift thing it can do - I push the inside lever a little bit (not allll the way across - just about halfway), there's a sort of pop, and the rub stops. I'm still not real clear on how it works - seems like that adjustment just magically becomes available when I need it.

I need to read up on it. And probably ask the bike shop folks for another tutorial.