1999 Plymouth Voyager Engine Idles Rough at Full Stop

Van starts right away and runs well until first put into Drive or coming to a full stop (in Drive). At that point there is significantly rough "idle" at about 600 RPM or so. If I put it into Neutral or Park, the vibration goes away. There is a little bit of rough idle in Reverse at full stop, but much less than in Drive. When I take my foot off the brake and begin driving, the engine runs fine.

Symptoms seem to be worsening over time. I had engine mounts replaced a couple months back, which lessened the symptoms somewhat, but they are back.

I have noticed very little loss of performance (for this age vehicle) and my mileage is still good (22+ mpg) relative to what it's been in the past.