ReadyLIFT customers have asked for it and we have delivered. In fall of 2018 we announced our new leveling and SST lift kit offerings for the all-new GM 1500 trucks. We specifically did not include the factory lift kit-equipped GMC AT4 and Chevy Silverado Trail Boss. The AT4/Trail Boss are factory equipped with a 2" front lift. This front lift includes a longer front shock/strut assembly. When combining a traditional leveling kit on these factory lifted trucks, several issues present themselves including binding problems with the factory control arm ball joint and contact concerns with the lower strut/CV axle assembly. The ReadyLIFT 66-3921 1.75" leveling kit is similar to our popular 66-3086 leveling kit for pre-2019 trucks. The 66-3921 leveling kit provides required amount of lift without causing conflict with the factory strut geometry and clearances. In light of the factory upper control arm's lack of dynamic range when the AT4/Trail Boss truck is further lifted, this leveling kit includes our popular tubular upper control arms with corrected ball joint cup angles, heavy-duty replaceable ball joints and out new Terrain Control Technology (TCT) maintenance-free pivot bushings with side-biter washers to improve alignment retention. Note: AT4 and Trail Boss do not fit the same size tire. This is due to the difference in front fender opening design. NOTE: Not compatible with Sierra AT4X or Silverado ZR2 Edition. 66-3921 Leveling Kit: AT4 - Max tire 275/60-20, 20x9 0 offset wheel Trail Boss - Max tire 295/65-20, 20x9 0 offset wheel