Darren,
The 3rd gen 4Runner 4wd system (since 1999) has a 50/50 split all the time (when you engage 4wd). It does not vary. I suspect that when you turn around a corner, the system "gives" allowing for different wheel speed between the front and rear axles. This system is similar to Torsen T-2 system.
The Torsen system (T-3 design in 4th gen 4runners) is better than ours ONLY in handling at high speed where a rear bias of torque is preferred. For example, that is why BMW X5 sends more torque to the rear wheels, instead of 50/50. Same goes for most 4x4 sports car. This is to promote gradual oversteer, rather than understeer, which is important in handling.
However, for a 5000+ lbs of steel that is high off the ground, i don't see much benefit in the rear bias Torsen system. Maybe with the new '03 4Runners, Toyota is envisioning a more sporty truck. It is also a great advertising proclamation: "4Runner is the first SUV in it's class to have the Torsen center differential."
The Torsen does NOT help in off-roading. In off-roading, you would lock the center diff, which will then distribute torque 50/50.
The A-TRAC system is the equivalent of having Limited-Slip Differential front AND rear axles. It is not going to be as efficient as an aftermarket locker system front and rear (aka. Detroit's) over severe terrain (rock climbing, deep mud). But, then again, with ATRAC, you don't have to worry about turning the lockers on and off while off-roading.
For more information on the '02 4Runner, try this thread:
http://www.toyota-4runner.org/showth...?s=&threadid=4
Thanks.