My theory:
You may have a sticky or bad Park Neutral Safety switch.
I am thinking your computer is being told after you get moving, that it is in gear now. No... In gear now. I mean now... Over and over again, so it keeps trying to lock when at speed above 8 mph. Could be wiring or connection to that switch too. The switches are about $40-50.
Try turning that feature off and see what happens (Mode 3 below, programmed through the DIC using the steering column menu/Enter/select buttons).
Excerpts from my 04 Owner's Manual....
Programmable Locking Feature
The automatic door locks were pre-programmed at the
factory to lock all the doors when the transmission is
shifted into gear. The following instructions detail how to
program your door locks differently than the factory
setting. Choose one of the three programming options
listed above before entering the program mode.
The following is the list of available programming
options:
Mode 1: All doors lock when the transmission is shifted
into gear.
Mode 2: All doors lock when the vehicle speed is
greater than 8 mph (13 km/h).
Mode 3: No automatic door locking.
Programmable Unlocking Feature
The automatic door locks were pre-programmed at the
factory to unlock the driver’s door once the transmission
is shifted to PARK (P). The following instructions detail
how to program your door locks differently than the
factory setting. Choose one of the four programming
options listed above before entering the program mode.
The following is the list of available programming
options:
Mode 1: Driver’s door unlocks when the transmission is
shifted into PARK (P).
Mode 2: All doors unlock when the transmission is
shifted into PARK (P).
Mode 3: All doors unlock when the key is removed
from the ignition.
Mode 4: No automatic door unlock.