This Explorer XL, either a 92 or a 93 with the 4.0 and an automatic, 150k, has
a strange problem.  When it has not been driven for a while, the transmission
will randomly slip into neutral while driving, usually uphill.  In order to get
it moving again, it is necessary to shift into park (neutral is not
sufficient), race the motor for approximately 10 seconds, and then shift back
into drive.  Shifting directly to park and then back into drive is not
sufficient either.  The problem is completely eliminated by allowing the motor
to warm up until the thermostat opens before driving it, i.e. it has never
slipped out under this condition.  This has been going on for at least 10,000
miles.  It acts the same in 4x4.  The transmission has been maintained with new
fluid as required.

Any thoughts?  I'm wondering if there are any known computer or control system
issues out there, but I suspect the torque converter.  The problem is mostly
annoying rather than serious, so more invasive diagnosis isn't really
justified.  I'm also wondering if it is likely to be doing any damage when it
pops out of gear or not.