I recently purchased a 2004, GMC Yukon XL Denali. Can anyone tell me about or point me to technical information about the components used in the AWD system of this vehicle? i.e. What type of center differential is used? Who makes the center differential? How is the torque balanced front to rear and side to side and to what extent or what percentages? What is the description of the fluid used in the center differential? Is it a synthetic or semi-synthetic fluid? Any help understanding this drive system is greatly appreciated - thanks!