My rear DR is doing something new to me. I have an Ultegra 6800 group set. I noticed it was having trouble shifting from the 2nd to 3rd biggest rear cogs when in the big chainring. It wants to stay in the bigger fear (under-shifting?). Other shifts worked fine, and the 2-3 shift works well in the small chainring. If I adjust the barrel nut in the shift cable to fix this, then the bike over-shifts at the small end of the cog set 8-9, 9-10. 10-11 works fine, probably because of the limit screw. Any ideas how to adjust this back to where it should be?

If I understand correctly, the problem is going from the larger cogs to the smaller cogs of your cassette? So as you release cable tension by shifting, allowing the RD to return to low-normal, it tends to not move. That indicates binding cables as a first, and easiest guess.

Increased cable friction would also be my guess, but without knowing how old the cables are, it would only be a guess. Ultegra cables have a low friction coating that could wear off in time increasing cable friction. Since this is the third year that Ultegra 6800 components have been on the market, the cables could be up to three years old and it may be time to change them

Cable friction would be my first guess too.

If I were working on your bike at home, the FIRST thing that I would check would be the derailleur hanger alignment with my gauge. It doesn't have to be very far off to cause the kind of problem that you are describing. Hanger alignment only takes a couple of minutes to check and, even if it's spot on, it's good to eliminate that as the possible source of your shifting problem.

Thanks for the replies. I loosened the cable, lubed it, and reset it. Feels much better. The cable itself only has about 2200 miles and was new in December, so it's not that old, but it certainly could be dirty.

The cable may have been changed, but was it the same as the original equipment one? I ask because this is something that is becoming increasingly important.The coating on Shimano cables for 11 speed drivetrains Is partially what solved the problems that plagued 10 speed shifters with cables routed under the bar tape

That's a good question. I will need to ask my lbs. they built up the bike using my old parts on a new frame in December. I know they used new housings and cables, but I just assumed they were good stuff. They have a good rep and have never steered me wrong, so I suspect they used high quality stuff. The cables are internally routed, not sure if that matters.

Agreed, if we had one handy. I'm thinking about making my own, or as one of the last tools purchase to round out the kit. A nice LBS can check and straighten the hanger for about $10. While you wait if during the really slow days...l