2007 Chevrolet Silverado 1500 Pickup Owner's Manual - Page 140

Automatic Transmission Operation If your vehicle has an automatic transmission, it features an electronic shift position indicator within the instrument panel cluster. This display must be powered anytime the shift lever is moved out of PARK (P). See Fuses and Circuit Breakers on page 598. There are several different positions for your shift lever. See "Range Selection Mode" later in this section. PARK (P): This position locks your rear wheels. It is the best position to use when you start your engine because your vehicle cannot move easily. If your vehicle has the Allison Transmission®, with the Power Take-Off (PTO), use PARK (P) when starting. The Allison Transmission® has a park pawl that is designed to hold the weight of commercial medium duty trucks. Therefore, the Allison Transmission® uses larger parts than other automatic transmissions. These larger parts may sometimes make a clunking noise when the selector lever is moved from DRIVE (D) or REVERSE (R) to PARK (P). This is normal and there is no damage occurring during these shifts. When parked on a hill, especially with a heavy load, you may notice an increase in the effort to shift out of Park. See Torque Lock (Automatic Transmission) under Shifting Into Park (P) (Automatic Transmission) on page 171 for more information. Automatic Transmission Allison Transmission® 140