Nissan Repair: cooling fans, nissan altima, cooling fans

Question
I have been experiencing problems with my fans running while i'm driving and a few minutes after the car is off.
I have a 1997 Nissan Altima Gxe, 2.4l, auto trans w/A.C.

I thought it was a faulty thermostat and replaced it. I have also replaced the radiator and the coolant sensor and still experiencing this problem.  Also the fans work as they should as long as it is just idling in the driveway to operating temp. but soon as i drive it somewhere they come on and stay on until a few minutes after shutting off,  PLEASE help me.
 P.S. i have checked all relays and the reference voltage for the sensor.

Answer
Chris,

If the fans stay on after the car shuts off it could be the relay that activates them.  I would switch out the relay first since it is the most cost effective item to change out.  But, if the fans are coming on and staying on it could be the temperature sensor that tells the computer to ground them.  Also, if you had the thermostat replaced and it is running hot it will keep the fans on to cool the engine.