@deep_sky - i would concede that part of the problem might be user-related (i.e. me); however, that does not explain why it worked well for me the past few months but does not now. i haven't changed my shifting technique at all, yet my derailleur doesn't work nearly as well as it has in the past. something has clearly changed on my bike.

additionally, the mechanic only rode it up & down the street (couple blocks each way). and honestly, there are times when i can get it to work on 3-4 shifts in a row; it's just not consistent. but more pertinently, i've had two other mechanics ride my bike in the past few days & they agreed that something clearly wasn't working ie the chain wasn't ramping up to big chainring. they just couldn't figure out why.