How can I disengage the security system and make the truck driveable again?

Does not sound like a security issue. It sounds more like an ignition switch issue. Even if your security system was failing, you would have all other functions except the starter would not work.

Roy

Password Learn Procedure For Anti-Theft System

Password learn procedure must be performed if Vehicle Control Module (VCM), passlock module or passlock sensor is replaced. A password is communicated between VCM and passlock module to provide engine operation. If VCM is replaced, the VCM must learn the password from the passlock module.
Momentarily rotate ignition switch to CRANK position, but do not start engine. Release switch to RUN position, but do not turn off. Wait 10 minutes and observe SECURITY indicator.
NOTE:Ensure battery is fully charged before proceeding. Ensure steps are followed in correct order or procedure may need to be repeated.

If passlock sensor was replaced, SECURITY indicator will flash for 10 minutes. If passlock module was replaced, SECURITY indicator will flash for a few seconds, then remain on for 10 minutes. If VCM was replaced with a new programmed VCM and connected to vehicle for the first time, vehicle will start and this procedure is not necessary. If replacement VCM was connected to any vehicle at any other time, SECURITY indicator will flash for a few seconds, then remain on for 10 minutes.
Of ignition remains on, SECURITY indicator will transition from flashing on briefly to off after 10 minutes. Turn ignition off and wait 10 seconds.
Repeat programming procedure 2 more times. New security code is ready to be communicated. New password is learned on next ignition switch lock cylinder from OFF to CRANK to ON.