Fluid low?
Or sticky valve body - When did you last change the trannny fluid?
(You mean it needs to be changed????)
** Posted from http://www.teranews.com **

Low fluid level. It expands as it heats up, which thereby gives you the
volume necessary for proper function (like shifting into gear). To check the
fluid level, warm up the car (preferably with some driving rather than just
idling, as that will warm the ATF faster), put it in Park, pull the tranny
dipstick, wipe it clean, reinstall (all the way in) and pull out again. If
you're lucky, your tranny will not have gotten too far along the path to
self-destruction yet...

Fluid level was fine but looked brown instead of red so I decided to a
fluid/filter change.  There was some metal chunks in the bottom of the pan
and everything was covered with a black like film.  I am hoping the drain
valve was just gummed up, allowing the torque converter fluid to drain out
overnight, since it would only happen in the morning.  That combined with a
dirty filter and fluid, maybe its fixed.  Kinda concerned with the metal
chunks though!?!