GMC 1999 Jimmy Owner's Manual page 232

CAUTION:
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.
CAUTION:
Coasting downhill in NEUTRAL (N) or with the
ignition off is dangerous. Your brakes will have to
do all the work of slowing down. They 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. Always have your engine
running and your vehicle in gear when you
go downhill.
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D
Know how to go uphill. You may want to shift down
to a lower gear. The lower gears help cool your
engine and transmission, and you can climb the
hill better.
D
Stay in your own lane when driving on two
roads in hills or mountains. Don't swing wide or cut
across the center of the road. Drive at speeds that let
you stay in your own lane.
D
As you go over the top of a hill, be alert. There
could be something in your lane, like a stalled car
or an accident.
D
You may see highway signs on mountains that
warn of special problems. Examples are long grades,
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passing or no passing zones, a falling rocks area
or winding roads. Be alert to these and take
appropriate action.
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lane