What could be screwing up my shifting?
 

I have a Felt F-35 (double-crank 39/53 and nine-speed cassette 12/27) with a mixture of Ultegra and Dura Ace stuff for the most part.

I usually have a problem shifting DOWN from 7th gear to 6th on the cassette (moving to a bigger cog). There has only been a few periods when it seemed to shift well and when it did, usually a week or so later it was back to having problems.

Sometimes it is just a longer delay than any other shifting situation, but sometimes it just doesn't make that particular downshift at all or takes VERY long to change (like 20 seconds or more). I can get it to shift if I push the lever over a little extra, but I shouldn't have to do that, should I?

Anyway, consider this recent pattern of events:

1. Had a complete tune-up and everything worked GREAT.

2. After 3 rides of about 50 miles, the old problem came back - this time just a longer delay - so I was thinking I could just turn that adjustment screw in the back a little to the inside and it would be fine again EXCEPT that once or twice there was a delay shifting up (not sure which gears). But after a few days of mainly a dowshift problem, I turned the screw a little. Well, I had lots of upshift problems so I turned it back.

3. Got it back in the shop today and decide to go ahead and replace the chain. Same problem on the test ride except it sometimes didn't shift down at all to 6th without an extra push. We did several more test rides after various adjustments - same result. Replaced a cable, but still a problem.

4. The mechanic (a good one) took it out a couple times and made more adjustments. I'm not sure what he experienced, but then he had the shop owner try it. He said it shifted fine for him, but when I tried it, it still didn't work. He went through more small adjustments and finally it seemed better, though not great.

5. But riding home, when I had many more chances to test it, the problem was back.

I stopped by another shop which is supposed to have the best mechanic. He couldn't work on it then, but I asked him about the basic problem, pointing out the same gears gave me trouble on my prior bike (Bianchi Volpe).

He did say that Shimano sometimes did have places where shifting was not as crisp, but it should still do the shift even if a little slower than normal. Well, mine doesn't necessarily do that and often if it is just a delay, it is a real long one.

Since the other shop owner didn't have trouble, I also wondered if most cyclists just have developed a habit of pushing the lever over a bit extra when downshifting while I don't. Usually if I just move it enough to click, it won't shift right or maybe not at all.

Anyone have any ideas at all? Obviously it is possible to get it working right, since it has a few times, but it must be extremely touchy since it is rarely really good and never stays that way long.

Usually a delay in shifting tells me the cable is sticking or binding somewhere.

Except that it has happened so much, even very shortly after I first bought it as well as after prior cable changes (twice I've had that cable replaced with the problem still there).