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?