2008 GMC Sierra 1500 Pickup Owner's Manual - Page 280

When driving across an incline that is not too steep, the vehicle can hit some loose gravel and start to slide downhill. If you feel your vehicle starting to slide sideways, turn downhill. This should help straighten out the vehicle and prevent the side slipping. However, a much better way to prevent this is to get out and "walk the course" so you know what the surface is like before you drive it. Stalling on an Incline {CAUTION: Getting out on the downhill (low) side of a vehicle stopped across an incline is dangerous. If the vehicle rolls over, you could be crushed or killed. Always get out on the uphill (high) side of the vehicle and stay well clear of the rollover path. If your vehicle stalls when you are crossing an incline, be sure you, and any passengers, get out on the uphill side, even if the door there is harder to open. If you get out on the downhill side and the vehicle starts to roll over, you will be right in its path. If you have to walk down the slope, stay out of the path the vehicle will take if it does roll over. 4-22