raise and lower...ALL IN ONE!

Ok, so the title may not be as catchy as my question, but if it made you click on my thread, maybe you can answer! I'm looking for an air lift/lower suspention. I purchased a set of off-road tires (32/350x20's i'd put the rating but I can't remember what it is off hand) and the truck came with a set of Hankook Ventus with 20' Boss Motorsport rims...I don't have the factory rims. Now here's what I want to do. Get an air suspention that I can lower it below stock height for when I'm cruisin around the city and raise it for when I do some four wheelin' and swap out the tires, if that's possible to have a 2-in-1 system like that. From what I can tell, I can only have either/or, not both. I can either lower it from stock height and back again, or raise it from stock height and back again, which isn't what I want to do...I want the best of both words (cake and eat it too?). If anyone has any info, at least a name, of a company who manufactures such a design, can you let me know? At least someone who may be able to custom make this idea?

Thanx in advance.