NOTE: Use of Auto 4 HI feature not recommended.. NOTE: This GM 1500 kit is NOT COMPATIBLE with vehicles equipped with rear composite mono-leaf springs. The mono-leaf is easily identifiable the U-bolt is round/circular around the top of the leaf spring. This kit only works with vehicle equipped with traditional steel leaf springs identified by square U-bolts. NOTE: Not compatible with Sierra AT4X or Silverado ZR2 Edition.