GMC 2004 Sierra 1500 Pickup Owner's Manual page 426

Get the vehicle warmed up by driving about 15 miles
(24 km) when outside temperatures are above 50°F
(10°C). If it's colder than 50°F (10°C), drive the vehicle
in THIRD (3) until the engine temperature gage
moves and then remains steady for 10 minutes.
A cold fluid check can be made after the vehicle has
been sitting for eight hours or more with the engine off,
but this is used only as a reference. Let the engine
run at idle for five minutes if outside temperatures are
50°F (10°C) or more. If it's colder than 50°F (10°C), you
may have to idle the engine longer. Should the fluid
level be low during this cold check, you must check the
fluid hot before adding fluid. Checking the fluid hot
will give you a more accurate reading of the fluid level.
Checking the Fluid Level
Prepare your vehicle as follows:
•
Park your vehicle on a level place. Keep the engine
running.
•
With the parking brake applied, place the shift lever
in PARK (P).
5-26
•
With your foot on the brake pedal, move the shift
lever through each gear range, pausing for about
three seconds in each range. Then, position the shift
lever in PARK (P).
•
Let the engine run at idle for three minutes or more.
Then, without shutting off the engine, follow these
steps:
The transmission dipstick
handle with the graphic is
located at the rear of
the engine compartment,
on the passenger's side.