So I finally figured out that the park/run IAC offset was too low and added a few steps. Now it idles at 765 regardless of gear selector position. I guess with it too low, the ECM was giving almost as much air in park/neutral as it was in drive, causing the park/neutral idle to be too high. I enjoy learning on my own, but sometimes a little bump in the right direction is helpful...
Please chime in if I'm misunderstanding how that offset was affecting things.