GMC Sierra Classic 2007 Owner's Manual page 196

Read the instructions completely before attempting
to program the transmitter. Because of the steps
involved, it may be helpful to have another
person available to assist you in programming the
transmitter.
Be sure to keep the original remote control
transmitter for use in other vehicles, as well as, for
future programming. You only need the original
remote control transmitter for Fixed Code
programming. It is also recommended that upon
the sale or lease termination of the vehicle,
the programmed buttons should be erased for
security purposes. See "Erasing Universal Home
Remote Buttons" later in this section.
When programming a garage door, it is advised to
park outside of the garage. Be sure that people
and objects are clear of the garage door or
security device you are programming.
Programming Universal Home
Remote — Rolling Code
Most garage door openers sold after 1996 are
Rolling Code units.
196
Programming a garage door opener involves
time-sensitive actions, so read the entire procedure
before you begin. If you do not follow these
actions, the device will time out and you will have
to repeat the procedure.
Follow these steps to program up to three devices:
1. From inside the vehicle, press the
two outside buttons at the same time for
one to two seconds, and immediately
release them.