GMC 2003 Sierra - Manual (Page 367)

Turn Signals When Towing a Trailer
The arrows on your instrunner^t panel will (lash whenever
you signal a turn or lane ctiange. Property hooked up,
the trailer lan^ps will also flash, lelllrig other drivers
youTa about to turn, change lanes or stop.
When towing a trailer, the arrows on your inslnjment
panel will flash tor (urns even it the bulbs on the trailer
are burned out. Thus, you may
lliink
drivers behind
you are seeing your signal whan they ana not. It's
important to chec^ occasionally lo be sure the trailer
bulbs are slill working.
Driving On Grades
Reduce speed and shift to a lower gear before you atari
down a long Or steep downgrade, it you don't shift
down, you might have to use your brakes so much lhat
they would gel hot and no longer work well.
If you have an automatic transmission, you can low in
DRIVE (D). You may want to shift the transmission
to lower gear selection if the transmission shifts too often
[e.g., under heavy loads and/or hilty conditiorE).
You may also wani to act!vale the tow/haul mode if the
transmission shifts too often. &ee
Tow/Hsai Mods
LigN on 3‘4S.
(i you have a 5-spead manual Iransmtasion and you are
towing a trailer, It's better not lo use FIFTH fS) gear.
Just drive in FOURTH (4) gear (or, as you need
to, a tower gear).
If you have afi-speed manual transmission and ygu are
towing a trailer, it's betfor nol lo use SIXTH (6) gear.
Drive In FIFTH (5) gear {or. as you nead to, a lower gear)*
When towing at high altitude on sleep uphill gradeSf
consider the following: Engine coolant will boil at a lower
tampsrature than al normal attitudes. If you turn your
engine off immediately after towing at high altitude
on stsop uphrll grades, your vehicle may show signs
similar to engine overheating. To avoid this, let ihe
engine run while parked (preferably on level ground)
with the automatic transmission In PARK (P) {or
the manual transmission out ot gear ar>d
The parking
brake applied) fora few minutes before turning the
engine off. If you do gat the overheat warning,
see Bipioe Oversea f/np
on page 3-3S.
4-8S