Does anyone have any good advice or info on airbag suspension?

Okay, I am looking for information on Air Bags, and different ways to lower a truck. Here's the gist of what I want. I have an 09 chevy silverado that has already been lowered 2 inches in the front and about 3 in the back. I want to be able to drop this truck down about 2 more inches or so, and be able to keep the ride height the same as it is now. Obviously (at least to me) this is going to require a system to lower and raise the truck. Please be as specific as possible and any links you could provide to help would be great!