The truck went into a theft lock mode and had flashing lockout code on dash cluster?

So this can cause a procedural error for the security system. I would try a reset process.

Here is a guide to help reset the system:

https://www.2carpros.com/articles/step-by-step-guide-performing-a-hard-system-reboot-for-your-vehicles-electronics-systems

If this doesn't work let's run the codes with a CAN scanner. You can get a CAN scanner (Controller Area Network) which will work on most cars from Amazon.

Here is a video to show you how:

https://youtu.be/u-4syLc-ifQ

Please go over these guides and get back to us.