Transfer Case, Transmission, Differentials?

I have a couple questions. I had my wife take my truck in to get the 30,000 mile maintenance done in Florida. The Chevy dealer said they would not drain and refill the transmission and transfer case. They said when they flush the transmission, the transfer case is included. Are they connected fluidly? Also, you don't have to touch the differentials until 100,000 miles? The dealer also reccommended to have the injectors flushed, is that a good idea on a diesel? That dealer also wanted an extra $42.50 to inspect the brakes when they rotated the tires. I told them they were out of their mind. Thanks!