The automatic lock keeps locking and unlocking while driving

change your central locking relay , the solder in the relay will have cracks in it and so open and close with the heat and the cold.

It's probably a bad input to the BCM - body control module ! Have it checked for DTC'S - diagnostic trouble codes .
The automatic door lock function can only be enabled by the body control module (BCM) if the driver door open switch and door ajar switches are in the Closed state. For information on programming the automatic door locks, refer to Vehicle Personalization in Personalization.
DTC B3064 or B3069
DTC B3127
DTC B3128, B3133, or B3138
DTC B3132
DTC B3137
DTC B3272
Your best bet , take it to the chevy dealer . Unless you own a GM factory Tech 2 scan tool an have access to factory sevice repair info.
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The outputs to the door lock actuators are controlled by the body control module (BCM). When the BCM receives a lock input from a door lock switch, or a keyless entry transmitter, it applies battery positive voltage to the door lock actuator lock control circuit, a ground to the door lock actuator unlock control, and the driver door lock actuator unlock control circuits. When the BCM receives an unlock input from a door lock switch, it applies battery positive voltage to the door lock actuator unlock control, the driver door lock actuator unlock control circuits, and a ground to the door lock actuator lock control circuit . When the BCM receives an single Unlock input from a keyless entry transmitter, it applies battery positive voltage to the driver door lock actuator unlock control circuit and a ground to the door lock actuator lock control circuit to unlock the driver door. A second Unlock input from the transmitter applies battery positive voltage to the door lock actuator unlock control circuit, and a ground to the door lock actuator lock control circuit to unlock the passenger doors.

This diagnostic procedure supports the following DTCs:
• DTC B3128 Left Front/Driver Door Unlock Circuit High
• DTC B3133 All Door Unlock Circuit High
• DTC B3138 All Door Lock Circuit High

you don't, all your locking system, security everything runs through this system. you have 1 actuator (could be a rod) that tells your computer is locked is not working, that is all

lock and unlock use different relays

it sounds like you may have a door switch going bad or in need to adjustment, the car thinks the door is ajar and then cycles the locks. the hard part may be to figure out which switch is making it act up.

replace both door lock actuators to fix problem.

you have a short in the locking system.

Yes, there is a way to reprogram your car to lock the doors when the gear selector is put into Drive.
Follow this site for a complete step by step re-program of the door locks:
http://www.nialtima.com/automatic_door_locks-113.html

Dude, the same thing happened with my EL falcon. It turned out to be the key fob! The buttons were sometimes sticking and all of a sudden it would re-lock. Ususally it would unlock then immediately relock. Leaving no time to get into the the car. Sometimes we would be driving and the Alarm would go off without touching a thing. I ditched the Key Fob and all was well again.
I hope this helps

The left front door lock is faulty and needs replacing. Quite a common fault costs about £200 to fix approx . Regards