The Hellwig EZ-990 Medium Duty Helper Spring kit is great for medium duty loads. Simply mounts under the factory axle U-Bolt plates to help restore sagging springs and stabilize your vehicle. These helpers come as a pair and have a million mile warranty.
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I have had these on my 2008 Dodge 1500 4WD Big Horn for several years now. I routinely load the truck down to near max weight rating and have no trouble with the back end sagging at all. Installation was pretty simple but you do need a torque wrench so be prepared for that. Driving loaded or unloaded is pretty good with these. Unloaded you can sometimes notice extra noise going over a large bump from the loose play but not noticeable at all loaded. I tend to forget these are even on there because I've had no issues. Thanks!