Chain "vibrates" on higher gears
"Vibration" could indicate a bad chain angle or a misadjusted derailer.  On the other hand, it's typical to have smoothest operation near the middle of the cluster and some very slight noise/vibration higher and lower.  Hard to say whether you have a problem or not without knowing the precise nature and severity of what you're experiencing.

Note that a chain will last roughly 2000mi or 3000km (+/- 50%).  After that it's sufficiently worn that it's beginning to cause excessive wear on the sprockets.  A rear cluster will last roughly 5000mi/8000km under normal use but will wear faster if a worn chain is being used.  Also, if you're on your third cluster your front chainring is likely fairly worn, though the condition of a single front ring is usually not a major issue.