2003 Chevrolet Impala Owner's Manual - Page 237

If you drive regularly in steep country, or if you're planning to visit there, here are some tips that can make your trips safer and more enjoyable. Keep your vehicle in good shape. Check all fluid levels and also the brakes, tires, cooling system and transaxle. These parts can work hard on mountain roads. Know how to go down hills. The most important thing to know is this: let your engine do some of the slowing down. Shift to a lower gear when you go down a steep or long hill. Coasting downhill in NEUTRAL (N) or with the ignition off is dangerous. Your brakes will have to do all the work slowing down. They could of get so hot that they wouldn't work well. You would then have poor braking oreven none going down a hill. You could crash. Always have your engine running and your vehicle in gear when you go downhill. If you don't shift down, your brakes could get so hot that they wouldn't work well. You would then have poor braking or even none going down a hill. You could crash. Shift down to let your engine assist your brakes on a steep downhill slope. 4-24