Hmm, thanks for the helpful ideas and suggestions - in no particular order:

- the FD is a Campy Chorus braze-on double, got it used, not sure how old probably 2000 or newer.

- the front shifter is Campy Record Ergo style shifter, also got it used, not sure how old but it seems pretty recent.

- The frame is ti so I don't think there's much flex happening there. But the cranks are alloy Veloce compact and the FD has some play in the cage (i.e. grab the cage between thumb and forefinger, and you can wiggle it a little, despite it being firmly bolted to the FD braze-on). So maybe there is some flex going on with the FD cage and the crankset.

- I may have bad shifting technique, but not sure how to fix for this issue ... I was reaching a "kitchen sink" situation of trying absolutely everything to downshift - pedal fast, slow, stop, start, more pressure, less pressure, keep changing it up until the darn thing shifted in front. What sometimes helped the front finally downshift was, if I radically crossed the chain by shifting the rear to the biggest/innermost cog while the front was still on the big ring, with the FD grinding against it.

- "Try shifting while spinning the cranks under no pressure... I'll bet the problem goes away." Yes, exactly. On the bike stand, or going fast, or cruising on level ground, it shifts flawlessly.

- "if your FD has weak springs in it, the least little hill can put you into a situation in which you're trying to shift the FD while putting pressure on the pedals and it just won't go. Does it shift as soon as you let up on the pedals and let them spin for a couple of revolutions?" Um, hard to say. The FD's failure to shift only occurs on uphills, when I'm going slow and I don't have much margin to let up on pedal pressure.

- Somehow I think "weak springs" is on the money. If the springs were stronger, this would not happen, right? Does FD spring tension descrease as the FD ages? Do I simply need a newer FD with higher spring tension?