1996 GMC Jimmy Owner's Manual - Page 207

On a long uphill grade, shiftdown and reduce your speed to around 45 mph (70 km/h) to reduce the possibility of engine and transmission overheating. If you have an automatic transmission, you should use DRIVE (D) when towing a trailer. Operating your vehicle in DRIVE (D) when towing a trailer will minimize heat buildup and extend the life of your transmission. Or, if you have a manual transmission, it's better not to use FIFTH ( 5 ) gear, just drive in FOURTH (4) gear (or, as you need to, a lower gear). 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 you turn your engine off immediately after towing at high altitude on steep uphill grades, your vehicle may show signs similar to engine overheating. avoid this, let the To engine run while parked (preferably on level ground) with the automatic transmission in PARK (P) (or the manual transmission out of gear and the parking brake applied) for a few minutes before turning the engine off. If you do get the overheat warning, see "Engine Overheating" in the Index. You really should not park your vehicle, with a trailer attached, on a hill. If something goes wrong, your rig could start to move. People can be injured, and both your vehicle and the trailer can be damaged. But if you ever have to park your rig on a hill, here's how to do it: 1 . Apply your regular brakes, but don't shift into PARK (P) yet, or into gear for a manual transmission. Then turn your 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 regular brakes until the chocks absorb the load. 4. Reapply the regular brakes. Then apply your parking brake, and then shift into PARK (P), or REVERSE (R) for a manual transmission. 5. If you have a four-wheel-drive vehicle with a manual transfer case shift lever, be sure the transfer case is i n a drive gear -- not in NEUTRAL (N). 6. Release the regular brakes. ' A