GMC Chevrolet Tahoe 2003 Manual page 404

Then, without shutting off the engine, follow these steps:
See Engine Compartment Overview on page 5-14 for
more information on location.
1. Flip the handle up and then pull out the dipstick
and wipe it with a clean rag or paper towel.
2. Push it back in all the way, wait three seconds and
then pull it back out again.
5-28
The transmission dipstick
handle with the graphic is
located at the rear of
the engine compartment,
on the passenger's side.
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 area or cross-hatched area for a hot check.
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.