PS- this all makes sense given the gross weights of our vehicles
Yukon = 5,379-5,626 lbs. weight is 2wd - 4wd obviously
Yukon XL= 5665-5965 (porky pig) 2wd-4wd obviously
Sierra 1500 = 5,182 -5,509lbs weight is 2wd-4wd obviously
The SUV + 4wd versions of either are heavier and therefore...