2009 GMC Canyon Owner's Manual - Page 246

When towing at high altitude on steep uphill grades, consider the following: Engine coolant will boil at a lower temperature than at normal altitudes. If the engine is turned off immediately after towing at high altitude on steep uphill grades, the vehicle may show signs similar to engine overheating. To avoid this, let the engine run while parked, preferably on level ground, with an automatic transmission in P (Park) or a manual transmission in N (Neutral) with the parking brake applied, for a few minutes before turning the engine off. If the overheat warning comes on, see Engine Overheating on page 5-32. If parking the rig on a hill: 1. Press the brake pedal, but do not shift into P (Park) yet for vehicles with an automatic transmission, or into gear for vehicles with a manual transmission. Turn the wheels into the curb if facing downhill or into traffic if facing uphill. 2. Have someone place chocks under the trailer wheels. 3. When the wheel chocks are in place, release the brake pedal until the chocks absorb the load. 4. Reapply the brake pedal. Then apply the parking brake and shift into P (Park) for vehicles with an automatic transmission or into gear for vehicles with a manual transmission. 5. If the vehicle has four-wheel-drive, be sure the transfer case is in a drive gear and not in N (Neutral). See Four-Wheel Drive on page 2-26 for more information. 6. Release the brake pedal. Parking on Hills { CAUTION: Parking the vehicle on a hill with the trailer attached can be dangerous. If something goes wrong, the rig could start to move. People can be injured, and both the vehicle and the trailer can be damaged. When possible, always park the rig on a flat surface. 4-56