2003 GMC Yukon Owner's Manual - Page 119

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 shift 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. Tow/Haul Mode Notice: Spinning the tires or holding the vehicle in one place on a hill using only the accelerator pedal may damage the transmission. If you are stuck, do not spin the tires. When stopping on a hill, use the brakes to hold the vehicle in place. On cold days, approximately 32°F (0°C) or colder, your transmission is designed to shift differently until the engine reaches normal operating temperature. This is intended to improve heater performance. Your vehicle may be equipped with a tow/haul mode. If so, the selector button is located on the end of the column shift lever. You can use this feature to assist when towing or hauling a heavy load. See Towing a Trailer on page 4-61 for more information. 2-25