'95 Park Ave Herky-jerky continues

This is the next episode of the "herky-Jerky" problem with our 95 Park Ave. Briefly, the car sort of loses power momentarily, making the car do
what I call the herky-jerky. This is an intermittent thing, mostly at freeway speeds... 60-70 mph. I believe it is an engine missing problem, causing the torque converter clutch (TCC) to engage/disengage, thus amplifying the effect at the wheels. Throughout all of this (several months now) the Check Engine light never came on UNTIL TWO DAYS AGO. Read on...
Here's what's been done so far:
Plugs and secondary wires replaced. Did this myself. This gave immediate improvement, but the problem returned and worsened a couple weeks later. Discovered one of the new plugs had stopped firing. Replaced it, with immediate positive effects.
Air Mass Flow sensor replaced. This was done when the problem returned after the bad plug was replaced. No effect at all.
Took the car to a GM dealer where they supposedly had "all the right diagnostic equipment." Wrong. They found nothing for $88.
Back at the independent garage, fuel filter and pressure regulator replaced. This was done after testing rail pressure. I checked it at idle, getting a reading of 34 PSI. I was advised here (and by my garage) that 41-47 was normal. I thought this fixed the problem because we did not experience the problem for a few days.
Then two days ago it started doing it again on the freeway. I now suspect the fuel pressure thing was a red herring, as a careful reading of AllData (which I finally subscribed to for $25) I see that the 41-47 pressure is the correct range after letting the pump run a few seconds by turning the ignition on but NOT starting the engine. At idle, it can be 6-10 PSI less and still be in spec. So, there was probably nothing wrong with the regulator. The reason I thought the problem was fixed was we had not been doing any freeway driving. BTW, the problem might not happen until 10-15 miles of driving, so when the techs drive it they are quick to proclaim "it's OK."
Now the new development. The same day that we had the freeway herky-jerky we went out to dinner in the evening. Right after backing out of the garage, the Check Engine light came on. Don't think it had ever happened before, as we both said "What's that?" It went off for a bit on the way to the restaurant, then cam back on and stayed on. Next morning I took it back to the garage, light on most of the way. The tech called after a bit and said it was a 171 error, Lean Running condition. Later in the day he called to say it was fixed, the problem being the O2 sensor wire too close to a spark plug wire. Unfortunately, the light came back on before we got home. Today, it's back in the shop, with the tech working his way down the diagnostic chart I suppose.
Two more things: (1) the Traction Off light also comes on occasionally. (2) the heater/AC is doing crazy things, i.e., hot air out the passenger side vents, cold out the driver's side.
I used to think my '76 Jaguar V12 was a problem car... weird things going wrong that no one could diagnose. After retiring I started doing my own maintenance on it (well, some of it anyway), and now think it's all pretty straightforward. I'm proud to say that on our way to recover the Park Ave from the garage my wife commented "this thing is running pretty good, isn't it?" Maybe one day I'll discover the Park Ave is straightforward too, but at this point it's hard to imagine.
Any further suggestions will be appreciated, and thanks for listening.
Ed
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Word from the tech is that they used the wrong air mass flow sensor when they replaced it a few weeks back! The Ultra is supercharged and apparently uses a different part. Of course the tech says the parts house supplied the wrong part....
Bad news is it's not available locally, so it will be Monday or later before we learn if this fixes. HOPE, HOPE , HOPE.
Ed

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