Control Trac is the system on the V6 models. Usually 90% of power goes to back wheels. If wheels start to slip more power is sent to the front. There is a switch on the dash that can lock it in 4x4 mode and a low range mode. This is computer controlled by switching an electric clutch on and off many times a second. The more it stays "on" the more power sent to the front. In 4High or
4low the clutch is basically on all the time.
In AWD there is a silicone clutch that works mechanically to send more torque to the front. Advantage of this is there are no electronics to break and it seems to be much smoother when it engages.
Disadvantage is you can't lock it in. Your wheels have to start spinning before it kicks in. With control trac you can lock it in 4x4 and torque goes to front and back before the back looses traction.
Also with control trac your dealer can install a nuetral tow option that lets you tow the explorer behind an RV without disconnecting drive shaft.