I'd rather be swimming...biking...running...and eating cheesecake...
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2008 Cervelo P2C Tri bike
2011 Trek Madone 5.5/Cobb V-Flow Max
2007 Jamis Coda/Terry Liberator
2011 Trek Mamba 29er
That's common. The bike will behave differently under load. Do you have a trainer? Sometimes I will work on tuning with my bike set up on the trainer with light resistance (enough that I can still hand pedal, but not so little that it's freely spinning).
Because you are getting stuck shifting in EITHER direction, it's probably a cable issue instead of a FD adjustment. Try lubing the cable well under the BB with any oily cleaning lube like Prolink. Lube/clean the shifter with WD-40. Have you always had this problem? How old are your cables? You might need new ones.
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"I never made "Who's Who"- but sure as hell I made "What's That??..."
Well cables don't last forever. There are a lot of factors involved in cable wear. If you've always had the problem with shifting, then it's probably not that the cables have suddenly died. But today I was out for a 50mi ride. Around mile 40, I had trouble shifting in either direction in the rear. It would take 2 or 3 tries each time. Being pretty sure that the cable was near toast, I quit shifting the rear until I reached the shop, which was conveniently located about 2 mi from the end of my ride. I asked them to replace the cable. When they pulled it out, the end inside the shifter was shredded and would have snapped soon.
More commonly, you will get some gunk (from your bottles or the road) near the cable stops under the BB or grunge and dirt down in the shifter. Too much friction means poor shifting, and it will seem worse under load.
It could also be that your shop didn't tune it well from the start, which might mean a combination of things like a too loose cable and a too tight lower limit screw.
I am going through a cleaning overhaul this week. I must admit that I haven't been very adamant about bike maintenance, considering I really don't know what I'm doing, but I'm learning!
I recall having a few shifting issues in the beginning, took it into the shop for my warranty tune-up but at that point I got injured and my ability to test out the shifting was limited. It is really hard to say when I starting seeing these issues, especially with my flat routes.
If the cleaning doesn't help, off to finding an LBS that I can whine to about my shifting woes.