What may cause a 1994 3000GT to stall only when it is driven and only after it is put into gear?

A 1994 3000GT may stall when put into gear due to issues such as a failing automatic transmission, which can lead to improper engagement and stalling under load. Additionally, problems with the fuel system, like a clogged fuel filter or failing fuel pump, can restrict fuel flow when the engine is under strain. Another possibility is a vacuum leak or a malfunctioning idle air control valve, which can disrupt the air-fuel mixture when the load changes. Lastly, issues with the ignition system, such as worn spark plugs or faulty ignition coils, could also contribute to stalling when the vehicle is driven.