i put a 3" body lift on a 2001. It may not be exactly the same for a 99, but FWIW, this is what I did (from what I remember)
- body spacers
- brake line extensions. The brake lines in the engine compartment are bolted to the body. Under the truck, they are bolted to the frame. You need a mounting extension for the transition
- bumper relocation brackets since the body goes up but the bumpers are mounted to the frame
- The radiator can move 3" but the shroud must remain centered with the fan which is mounted to the engine
- gas tank filler relocation
- Negative ground extension in the engine compartment
- gap guards to fill the space between the frame and the body.