Rear Derailleur is
not shifting properly. I've usually been able to keep one shifting correctly however this one has me a bit perplexed. I noticed today it would not shift down to the highest cog. I tightened the cable tensioner a bit and it seemed to shift fine. Several miles later I really encountered shifting issues. The chain is jumping between the highest cogs, and will not seat itself on the 13 gear. The L & H alignment look good as well as the B angle. Could it be solely related to cable stretch? Either way its beyond me. I'm headed to the LBS Monday. Lp