2003 GMC Sierra 1500 Pickup Owner's Manual - Page 115

Drive (D) can be used when towing a trailer, carrying a heavy load, driving on steep hills or for off-road driving. You may want to shift the transmission to THIRD (3) or, if necessary, a lower gear selection if the transmission shifts too often. Notice: If your vehicle is equipped with the Allision@ Transmission, do not idle DRIVE (D) for in more than five minutes. Extended idlingin DRIVE (D) may cause transmission overheating and damage. Always select PARK (P) if idle timeis longer than five minutes. If your vehicle is equipped with the Allison@ Transmission, it will initially attain first range when DRIVE (D) is selected. As vehicle speed increases, the transmission will upshift automatically through each available range up to FIFTH (5). As the vehicle slows. the transmission will downshift automatically. If you manually select SECOND (2) in a light duty automatic transmission, the transmission will drive in second gear. You may use this feature for reducing the speed of the rear wheels when you are trying to start your vehicle from a stop on slippery road surfaces. FIRST (1): This position gives you even more power (but lower fuel economy) than SECOND (2). You can use it on very steep hills, or in deep snow or mud. If the selector lever is put in FIRST (1) while the vehicle is moving forward, the transmission won't shift into first gear until the vehicle is going slowly enough. THIRD ( ) This position is also used for normal driving, 3: however it offers more power and lower fuel economy than DRIVE (D). SECOND (2): This position gives you more power but lower fuel economy. You can use SECOND (2) on hills. It can help control your speed as you go down steep mountain roads, but then you would also want to use your brakes off and on. Notice: If your rear wheels won't turn, don't try to drive. This might happen if you were stuck in very deep sand or mud or were up against a solid object. You could damage your transmission.Also, if you stop when going uphill, don't hold your vehicle there with only the accelerator pedal. This could overheat anddamage the transmission. Use your brakes or shift into PARK (P) to hold your vehicle in position on a hill. On cold days, approximately 32°F (OOC) or colder, your transmission is designed to shift differently until the engine reaches normal operating temperature. This is intended to improve heater performance. 2-28