Installation kits are essential when upgrading your GM 2500HD/3500HD with new gears, ensuring optimal and reliable performance. Our gear installation kits include all the necessary components such as shims, bearings, crush sleeves, and more, offering everything you need for a complete overhaul of your GM's front and rear differentials when switching to more aggressive gearing. Check out our excellent selection of Gear Packages. GM Duramax Fitments: 2006, 2007 GM 6.6L Duramax.Submodel Fitments: WT, Custom, LT, LTZ, High Country, 1LT, 2LT, Pro, SLE, SLT, AT4, Denali.Some exceptions apply, please see individual product pages for specific fitments.