'98 Club Wagon stalling at intersections

75K miles only. Seems to be running lean. This is a recent phenomenon. The stalling is only occasional, but happens only at very low speeds, following
deceleration. Car also pings under acceleration, on the freeway. I drive it gingerly to avoid the pinging. Pinging abates at night, for some reason. There is no overheating. Can anyone advise?
Before this stalling business, I was getting "P0401" code "insufficient EGR flow." Before I fixed that, but a couple months after P0401 started to show, I started to see the stalling. After I replaced the EGR flow sensor, which fixed the P0401 error, the stalling has gotten worse. And, to boot, NOW I am getting P0402 errors. Seems to be an inappropriate error code.
The P0401 was associated with noticeable sputtering upon acceleration at low speeds. This was conspicuous lean fuel-air mixture. A P0401 implies a mixture too rich, not too lean. As such, I still believe the error should have been "P0402," "excessive EGR flow," because THAT is INDEED what was happening. I used a vacuum gauge to observe the command signal to the EGR valve, before and after replacement of flow sensor. Replacing that flow sensor SOLVED that sputtering problem, immediately. I had previously taken the EGR valve out and found it to be OK.
So now the stalling is worse. I am about to put some serious instrumentation on the car, but thought I'd petition here for anyone who has experienced this problem.
Thanks
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I forgot to mention the engine is 5.4L V8. California vehicle. Engine has been extremely reliable over the years...until recently.
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