car stalls when any torque applied

My dad has a Ford Falcon AU auto that has stopped working…

1. The car is idling quite rough and has a tendency to stall.
2. If left to idle it’ll stall after a minute or so
3. You can rev it hard when it is in park and it’ll be mostly ok
4. if you put it into drive it’ll then move a forward slowly (normal for an auto)
5. as soon as the accelerator is applied while in drive it stalls

We’ve changed the spark plugs and replaced the fuel pump.