1997 Discovery automatic.
I have a very annoying intermittent problem which leaves me stranded sometimes.
Symptoms:
Won't move forward in drive, particularly when parked on a hill.
Won't idle smoothly when this happens.

Happens more when tank is low but not always.
On flat ground will eventually move when it is warmer, but randomly fails to move in Drive during a journey when I stop at a roundabout or point it toward a hill.
Yesterday it failed to move in Drive at a roundabout and wouldn't even click over. I clicked through the Park, Drive, N, 1,2 and 3 and then it started again and moved a short distance in Drive but then wouldn't move at all, but was running, so I left it where it was and walked to work.

Any clues??