Still did it after a key cycle? Often stuff is disabled until the next key-off when problems are detected.
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If it's not the transmission, and it's not the PCM, and it's not the tune file, what's left?
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If possible, backprobe between E & B at the 20-way with a load (brake light bulb or similar), still connected to the trans. Or tap in by piercing close to the 20-way if backprobing isn't possible. Command 3rd. Just verify the circuit can carry current without dropping out.
If it blinks or drops out, move one leg of the test light from 20-way B to battery positive. That splits the circuit in half, makes it easier to pin down which side the problem is on. If that's OK, put one leg back to 20-way B and other leg to chassis ground and retest (though a problem on 20-way B is unlikely, since it seems the other solenoids that share it are working).