Type of fluid in 1999 silverado transfer case?

it uses a brand by acdelco, and you have to order it from a dealer. its called auto trak 2. if you don't use this specific fluid it will mess up your transfer case, i learned the hard way. and they wont recomend it until you've already had problems , that's how they make their money, good luck, it runs about 6-10 dollars a quart.