E320 stalling in gear
 

For a while I have been noticing the idle speed of my '02 E320 dropping greatly and beginning to stumble when I go into reverse to back out of my driveway, typically during high idle warm-up when the engine is stone cold. Today the engine stalled within ~1 sec. of going into reverse (or drive) and jerked like "dropping the clutch" on a manual trans. This happened a few times, but eventually I got moving when I quickly accelerated as soon as the engine started. Also shifting R->N or D->N causes a serious thunk in the drivetrain. I replaced the flex discs a few months ago. Any ideas?