Replies to Pat, Mike, and D*Alex....

First off, thanks everyone for your replies!

Pat: Odd you should mention pulleys. When I recently pulled them off to clean them, it dawned on me that once I had them off they were different. The Ultegra came with two different kinds of bearings. One was a standard sealed bearing, the other was a plastic or ceramic bearing. The guys at my LBS checked it out and said I had returned them to the proper positions, but I'm not so sure. I've searched the Shimano www site but couldn't find out why there is a difference or which positions they should be in.

Mike: I'm not sure how to definitively confirm that a shifter is the problem here. Any advice? FWIW, I think the slips have always been small to larger cog in the rear but am not 100% sure, more like 99 & 44/100ths.

D*Alex: Re your first point, would you expect chainstay flex to be a problem with a CF frame? (The bike is a Trek 5200. FWIW, the bike has a bit more than 8,000 miles & a 200-lb rider, who wouldn't mind getting to 170 again, but that's another thread) And yes, the LBS really did change me to a brand new cassette. I watched the installation myself after inspecting the new cassette they took out of a display case. That's a good point, though, because I know of at least one shop that cheats on parts, but that was on the east coast when I lived in DE.

Thanks again,

Trekaholic