My 2015 GWM's engine starts but quickly cuts out

The fact that it sometimes runs perfectly means there’s nothing fundamentally wrong with the engine’s intrinsic bits and pieces. If there was, it would never run perfectly at all. Which means you’re probably chasing a sensor, fuel supply or electrical problem.

Cars like this have sensors all over them to inform the computer of what conditions demand, what the driver is asking for and what it should do about all of that. Scanning the car electronically might provide the answer via a fault code. But we’d also take a look at the engine’s stepper motor which is a small electric actuator that controls the throttle position. If this component is not working properly, it can lead to the exact symptoms you’re seeing.