Yes, The 00-06 Denalis come with torsion bars. You can crank the torsions to gain a few more inches of lift...or get new torsion keys. As well, there are kits that can raise your Denali.
The OEM "AIR RIDE" is a load leveling system. You put a trailer behind it, it adds air to level the truck. The system is not as "luxury" or fancy as you'd think though. Most of us that have lifted or lowered our Denalis and removed that system, added better shocks, and installed a helper bag system in the coils which allows us to add the amount of air that WE want.