Can anyone suggest what I may be doing wrong or what to look for? I changed out my 11-21 cassette to an 11-27 configuration for riding on the Blue Ridge Parkway last week and I had horrible shifting problems with my Shimano deraileur. In particular I could not get the chain to stay on the 3rd cog from the largest. I had no shifting problems with the original 11-21 and all other components remained the same. (same wheel, bike, everything the same). We tried adjusting the deraileur but to no avail. Once back home to flatter Michigan I exchanged the cogs and everything worked fine. Any suggestions would be helpful. This is a 9 speed Dura Ace cassette.
Ah, the Blue Ridge Parkway!!! I live in Virginia and love that ride. My initial guess would be the 11-27 3rd cog (the 21 tooth I believe) is worn more than the others and isn't quite meshing with your chain that would be newer/in better shape.