Personally, my new favorite for the back of a Chevy is the latest AirLift air bags that have a Sumo spring type overload inside them. You can raise the van with air bag part without getting a lot stiffer ride and still have a good bump stop inside the bag for the big bumps and dips.
For the front a spring change really is the best way. Moog makes a spring that should give you the amount you are looking for.
For the sway and control, a big rear sway bar is a very nice addition. Hellwig makes one that fits if you don't have a generator, and Roadmaster has on the will fit if it does have a generator.
All of these options have been covered extensively in several threads here.