What type of front differential fluid does the 2004 chevy trailblazer use?

The 2004 Chevy TrailBlazer needS75W-90 gear oil in the front differential. IAlso recommend that You use an additive for TBSS differentials. It is important to keep Your differential full because it is what offers the protection for Your gears. The differential is what distributes power to Your front wheels in this case, after the power comes out of the transfer case. If You happen to damage a gear then You will lose the ability to use four wheel drive and will need to replace it. A differential is a small place and all the power going through it can generate a lot of heat. This is why You will want to use a thick oil like 75W-90, it will break down much slower than a thinner oil.