This is how to program your 1999 (new body style), 2000, 2001, 2002, 2003, 2004, 2005, 2006, and 2007 GMC Sierra Pickup Truck replacement remote keyless entry fob alarm by yourself at home without going to the dealer.
Including 1500, 2500, and 3500 model trucks.
There is also a free programming tutorial video below to show you how easy it is done.

Obtain all remote transmitters.
Close all doors.
Insert key into ignition, do not turn ignition switch.
Press and hold door lock switch in the unlock position.
Switch ignition ON, OFF, ON, OFF.
Release door lock switch.
Doors will lock and unlock, indicating programming mode activated.
To program remote transmitter proceed as follows:
Simultaneously press and hold transmitter LOCK and UNLOCK buttons.
Doors will lock and unlock, indicating remote transmitter programmed.
Repeat above procedure for each remote transmitter.
Switch ignition ON to exit programming mode.
NOTE: Existing remote transmitter memory positions will be overwritten.
NOTE: A maximum of 4 remote transmitters can be programmed.