New to bike maintenance but want to learn. Recently bought a 2008 Schwinn Fastback Comp cheap. Has a Dura Ace rear derailer and cassette, but I'm having some problems with autoshifting -- not only up, but down, too. In fact, it even hops back and forth with the wheels in the air. When riding, it feels like chain slippage. Occurs exclusively on one or two of the middle cogs, though the teeth are in great condition.
Would love some help figuring this out. Video here: http://www.youtube.com/watch?v=n-7M33xtw-w