Best bear hunt ever!

[Bigshooter]

I'm far from an expert but my guess is it overheated and puked out the fluid through the overflow hole.  I had to run mine in 1st gear when driving around in the hills during hot weather or it would overheat.  And even running it in 1st gear it would still start to overheat if it was really hot out. 

Both times it overheated on me I was on out of state hunts.  Talk about being worried.

[MagKarl]

Unfortunately this is a very common problem with automatics in Fords.  I've personally seen it in my brother's Explorer and wife's Excursion.  Your transmission is fine, it just needs a new input seal.  It's one of those jobs with a $12 part that takes you 12 hours to replace, that's what it took me anyway when I did the Excursion.   2WD makes it easier, pull the transmission and then the torque converter and swap out the seal.  An ATV jack is handy for this job. 

[coachcw]

sounds like it got hot . Ive seen fords blow fluid right past the front seal when the cook . It might be a good idea to make sure the cooler is free flowing and the filter isn't plugged.