GMC 1993 Safari Owner's Manual page 259

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 506F (IO"C), drive the vehicle
in D (Third Gear) 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 8 hours
or
more with the engine off and is used only as
a reference. Let the engine run at idle for 5 minutes if outside temperatures
are 50°F (1 0°C) or more. If it's colder than 50°F (1 O"C), you may have to
idle the engine longer. A hot check must follow when fluid is added during a
cold check.
To check the fluid hot or cold:
0
Park your vehicle on a level place.
Place the shift lever in P (Park) with the parking brake applied.
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 P (Park).
Let the engine run at idle for three minutes or more.
Then, without shutting off the engine, follow these steps:
X3619
6-21