GMC Yukon Denali 2006 Manual page 336

3. Check both sides of the dipstick, and read the lower
level. The fluid level must be in the COLD area,
below the cross-hatched area, for a cold check or in
the HOT or cross-hatched area for a hot check.
Be sure to keep the dipstick pointed down to get an
accurate reading.
4. If the fluid level is in the acceptable range, push the
dipstick back in all the way; then flip the handle
down to lock the dipstick in place.
5-24
Consistency of Readings
Always check the fluid level at least twice using the
procedure described previously. Consistency (repeatable
readings) is important to maintaining proper fluid level. If
inconsistent readings persist, check the transmission
breather hose to be sure it is clean and unclogged. If
readings are still inconsistent, contact your dealer.
How to Add Automatic Transmission
Fluid
Refer to the Maintenance Schedule to determine what
kind of transmission fluid to use. See Recommended
Fluids and Lubricants on page 6-13.
Add fluid only after checking the transmission fluid while
it is hot. A cold check is used only as a reference. If
the fluid level is low, add only enough of the proper fluid
to bring the level up to the HOT area for a hot check.
It does not take much fluid, generally less than one pint
(0.5 L). Do not overfill.