2007 Chevrolet Silverado 1500 Pickup Owner's Manual - Page 173

Torque Lock (Automatic Transmission) If you are parking on a hill and you do not shift your transmission into PARK (P) properly, the weight of the vehicle may put too much force on the parking pawl in the transmission. You may find it difficult to pull the shift lever out of PARK (P). This is called "torque lock." To prevent torque lock, set the parking brake and then shift into PARK (P) properly before you leave the driver's seat. To find out how, see "Shifting Into PARK (P)" listed earlier in this section. When you are ready to drive, move the shift lever out of PARK (P) before you release the parking brake. If torque lock does occur, you may need to have another vehicle push yours a little uphill to take some of the pressure from the parking pawl in the transmission, so you can pull the shift lever out of PARK (P). Shifting Out of Park (P) (Automatic Transmission) Your vehicle has an automatic transmission shift lock control system which locks the shift lever in PARK (P) when the ignition is in the LOCK position. You have to fully apply your regular brakes before you can shift from PARK (P) when the ignition is in RUN. See Automatic Transmission Operation on page 140 and "Torque Lock" under Shifting Out of Park (P) (Automatic Transmission) on page 173. If your vehicle has an Allison Transmission®, the transmission has a park pawl designed to hold the higher weight of commercial medium duty trucks. Therefore, the Allison Transmission® uses larger parts than other automatic transmissions. 173