Since you are in Oz, you have the S50b30. 286Hp. (at the crank, about 230-240 rwhp)
Are you sure you are doing the stomp correctly? I'm not even sure that tthe stocp test even works on the Euro engine managment system. But..
Turn key to on, then immediately
Fully press gas pedal to the floor 5 times withing 5 seconds.'
Make sure that the pedal goes all the way to the floor, no carpet or mat blocking any travel? Check that the throttle linkage is letting the tb's fully open. (adjusted properly...
No matter where you go, there you are.