Boy am I embarrassed!
I continued looking for a single pipe control and found the "swell box amplitude" for D style was at the top (+36) for that pipe. I haven't attempted single pipe voicing. I did change trem. speed, but that is not per voice setting. I must have missed the pull down menu and that would default to middle C +36 on all voices. I still can't figure why it ever played, and will be more careful if I ever dabble in the voicing.
The 3-31 sounds great out of the box!