Some models equipped with the 4T60-E transaxle may exhibit a no movement condition, with the selector lever in the D4 or D3 ranges, but will move when the selector lever is placed into D2 or Lo range. When the engine RPM is increased with the selector lever in Park and/or Neutral, you may hear a noise that sounds like "Marbles in a an", but the vehicle still moves and shifts properly. Replace the OEM roller clutch springs with the heavy duty Sonnax springs K84956-SP. These springs successfully outperformed OEM springs in an ATSG sponsored test. As a result, this update is now recommended by ATSG as part of every rebuild for unit durability. Note: Not compatible with 1996-up black plastic roller clutch update.