This may not not apply to your truck as these instructions are for a 99+ NBS, but it may be worth a try. From what I've read it sounds like you need to have the BCM reprogrammed to get rid of this. I had the same thing with my 99 Yukon, it was annoying.
Beginning with the ignition in off, pull back on the turn signal/multifunction lever all the way toward you and hold it while you perform the next step.
turn your key to on and off twice. Then, with the key in off, release the turn signal/multifunction lever. Once you do this, you will hear the lock switch lock and unluck
You are now ready to program the automatic door locks. Select one of the following four programming options and follow the instructions. You will have ten seconds to begin programming. If you exceed the ten second limit, the locks will automatically lock and unlock to indicate you have left the program mode. If this occurs, repeat the procedures beginning with step 1.
The following is a lit of available programming options:
ALL DOORS LOCK/ONLY DRIVER'S DOOR UNLOCKS: press the lock side of the power locks switch on the door panel once and then unlocks side once.
ALL DOORS LOCK/ALL DOORS UNLOCK: Press the lock side of the power lock switch on the door panel once, then the unlock side twice (this is the factory setting)
ALL DOORS LOCK/NONE OF THE DOORS UNLOCK: Press the lock side of the power lock switch on the door panel once, and then the unlock side three times.
NO DOORS LOCK/NONE OF THE DOORS UNLOCK: Press the lock side of the power lock switch on the door panel twice. This turns off the automatic lock feature.