- New cassette is identical to the old (Shimano 11-34).
- I installed it intact as one unit.
- Visually the spacing looks perfect.
- A pro mechanic at Wheelworks looked at it for 5-10 minutes and didn't see anything wrong. I couldn't leave the bike, but we had a good conversation (he knew Sheldon Brown).
- New chain is identical (Ultegra).
- Rear derailleur is the same (Shimano M771 IIRC)
- Although I replaced the jockey wheels. (The RD has 13K miles, the wheel closest to the cassette was almost completely smooth)
BEFORE
- I could shift into all gears, although not the 11 sometimes because of the jockey wheel.
NOW
- It feels like 5 & 6 don't hook up properly, and sometimes the gear will change up/down for no reason. Gears 1-4 and 8-10 are solid. Occasionally 7 gets funky. I've tightened and loosened the barrel nut while riding, but it hasn't improved it.
I've changed lots of cassettes and chains, although the jockey wheels was a first. I am using a new computer, and I need to set it up better to upload pictures (after cropping and resizing using IrafanView).
And, I have not disassembled my rear wheel to take apart the cassette and inspect.
I am hoping that one of you brilliant guys will recognize the problem based on my description.