Originally Posted by Porkponey

Do you mean when you upshift (smaller cog) it downshifts immediately after, or do you mean it upshifts (smaller cog) less than smoothly. Or do you mean when you downshift (larger cog) it clunks loudly?

I have the same rear derailleur. Mine shifts ok, most of the time. If this is happening under power, let up slightly as you shift. With the small tooth gaps in my cassette, there are times when it will upshift so quietly, I won't know if it actually did or not. (It does.) Under power with no relaxing on the pedals, it bangs into gear. Letting off for a split second, it slips silently in. Kind of sucks the other way around though. It has never downshifted (easier gear, larger cog) very gracefully at all. I'm looking for a replacement.