I have a 2005 Yukon XL, purchased new. My window sticker and my build sheet both show that I have the Premium Smooth Ride suspension. What it doesn't say is if that is the ZW7 option. I've replaced the shocks w/OEM shocks once, but it's time do it again (188K miles). Other members have said Bilsteins are the only way to go. Every parts supplier as well as the Bilstein site say that if you order the 4600 series HD shocks, you also have to order the new rear springs (part #199020). It says that the ZW7 is the Nivomat Self Leveling Suspension. I don't know if that's correct or not - any help/advice out there?