useful tip about Seafoam, thanks!  I'll give it a try.  Does seafoam need to
be drained after doing its magic?

First I'll try Benny's advice of giving it time and a fluid top-up.  I was
being extra-careful to put in LESS than normal.

And thanks to Edward for the leveling suggestion -- our garage floor slopes
so maybe there's way less fluid than there should be.

Frank C. wrote:
>     Broken or disconnected flex drive plate ?

don't think so -- it was fine driving into the garage, so doubt it broke
while the van was stationary?  Actually, we had to have the flexplate
replaced last spring, when it broke over in Nevada, so it's sort-of-possible
that it could have gone again.  Would the TC spin if the flexplate was dead?
(I don't really know where the flexplate is -- will look in Bentley when I
get home tonight)