1999 Ford Taurus Tranny Problem

Hello all,
I have a 99 Ford Taurus with an electronic controlled automatic
transmission. The car has 115,xxx miles on it. It's been running fine except
for a few occasions when the transmission wouldn't shift. It happened 3 or 4
times in the last 6 months. The car would stay in 1st gear while the
engine's RPM kept raising to almost 5000 RMP and the car's speed was only
around 30mph (at this point, I let off the gas pedal because I was afraid
that something could be damage) This condition continued for several minutes
(5 to 8) before the transmission finally shifted to higher gear and
everything came back to normal.
Is this the first signs of a failing transmission? I 've checked the
transmission fluid level and it was OK. The fluid color looked pink red and
it didn't smell burned. The last transmission service (filter & fluid
change) was about 18 months ago...
What else should/can I check? How do I check the electronic shift control
module?
Any inputs are greatly appreciated.
Stanav.