2003 GMC Sierra 1500 Pickup Owner's Manual - Page 122

While you accelerate, it is normal for the light to go on and off if you quickly change the position of the accelerator. If your vehicle has four-wheel drive and is equipped with a manual transmission, disregard the SHIFT light when the transfer case is in 4-Wheel Low. Front Axle Locking Feature The front axle locks and unlocks automatically when you shift the transfer case. Some delay for the axle to lock or unlock is normal. Manual Transfer Case Ignore the SHIFT light when you downshift. Four-wheel Drive If your vehicle has four-wheel drive, you can send your engine's driving power to all four wheels for extra traction. To get the most satisfaction out of four-wheel drive, you must be familiar with its operation. Read the part that follows before using four-wheel drive. See the appropriate text for the transfer case in your vehicle. Notice: Driving in the 4-WHEEL HIGH (4HI) or 4-WHEEL LOW (4LO) positions for a long time on dry or wet pavement could shorten the life of your vehicle's drivetrain. The transfer case shift lever is on the floor to the right of the driver. Use this lever to shift into and out of four-wheel drive. 2-35