The ignition switch assembly performs three functions:

Unlocks the steering wheel
provides various voltages to start and run the truck
Provides a unique passlock resistance value to the BCM

When that resistance value is not present from the passlock module on the back of the ignition switch assembly then the truck starts but then stalls as the fuel injectors are cut off. A common hack is to take the passlock module out of the circuit and permanently present an acceptable resistance value to the BCM that is dependent on rotating the ignition lock cylinder. This solves a malfunctioning passlock system but does make the truck easier to appropriate.

Has the security light been blinking?

George