GMC 1995 Suburban Owner's Manual page 309

Wait at least 30 minutes before checking the transmission fluid level if you
have been driving:
0
When outside temperatures are above 90°F (32°C).
At high speed for quite a while.
In heavy traffic
-
especially in hot weather.
0
While pulling a trailer.
To get the right reading. the fluid should be at normal operating
temperature, which is 180°F to 200°F (82°C to 93°C).
To check transmission fluid hot: 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 (l0"C). drive the vehicle in DRIVE (D) until the
engine temperature gage moves and then remains steady for ten minutes.
Then follow the hot check procedures.
To check transmission fluid cold: A cold check is made after the vehicle
has been sitting for eight hours or more with the engine off and 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
(
IOOC), you
may have to idle the engine longer. Should the tluid level be low during a
cold check, you must perform a hot check before adding fluid. This will
give you a more accurate reading of the fluid level.
To check the fluid hot or cold
0
Park your vehicle on a level place. Keep the engine running.
0
With the parking brake applied, place the shift lever in PARK (P).
0
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 shi.ft lever in PARK (P).
0
Let the engine run at idle for three minutes or more.
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