2005 Chevrolet Silverado 1500 Pickup Owner's Manual - Page 117

The tachometer for both the diesel and gasoline engine shows a dashed red zone and a solid red zone. The dashed red zone indicates where a transmission shift occurs for full engine power. When using grade braking, the transmission's shift point is adjusted to just prior to the solid red zone, providing the benefit of additional engine braking. Grade braking driving within the dashed red zone is normal, both the diesel and gasoline engine have been designed for this grade braking feature. Do not allow the engine to go into the solid red zone. Apply the vehicle's brakes for a short time to slow down if you are driving on a long hill and the tachometer needle enters the solid red zone. See Towing a Trailer on page 4-69 for more information. Overdrive Disable (Allison® Transmission Only) If your vehicle has an Allison Transmission®, you may have the overdrive disable feature. The overdrive disable feature prevents the transmission from shifting into FIFTH (5) gear. The selector button is located on the end of the column shift lever. You can turn overdrive disable on and off by pressing and holding the button at the end of the column shift lever until the indicator light, on the instrument panel, illuminates. If your vehicle has both Tow/Haul and overdrive disable, tap the button once to enable or disable Tow/Haul, and press and hold the button to enable or disable overdrive disable. 2-31