I noticed somthing today.  While driving at highway
speeds I slightly lifted my foot of the excelerator
and saw a drop in engine RPM of about 1500 RPM. THe
car didn't immiediatly slow down.  I then decided to try
somthing.  I alternatly goosed the excelerator then
let off(never completely flooring it or totally letting
off)  I could vary the engine speed by about 1500RPM, but
the vehicle speed didn't immediatly respond.

This is a 97 Altima.  Auto transmission.
It this behaviour normal. (FWIW This is the first
auto tranny I have driven in almost 18 years.  All
my other cars have been 5 speeds)
Does this vehicle have a lockup torque converter?
How do I check if it's working?
Could there be a slip in some other part of the
tranny?