83 300 SD transmission question

My transmission was working fine and then I had a sudden failure.

It would come out of first (or perhaps second) and then into neutral. I
drove about 12 miles home on back roads and then I stopped at the post
office to pick up my mail. When I restarted the car it shifted.

This just happened, so I am not sure if it will shift tomorrow or not.
There was no expensive noises or anything so I assume that this is something
minor.

I read Richard Sexton's article about the B2 piston failure, but this
doesn't seem to be the same thing (not too sure however).

Any ideas?

Roger Shoaf
83 300 SD

I would also check the fluid for any abnormal smell or sediments.