i have a 2001 auto and i have just replaced the prop shaft. it was reasonably heavy so i think it was steel. both old and replacement were the same. However I have had a lot of vibration problems, and the main culprit was the main bearing in the gearbox extension housing which is no doubt not designed for a steel prop but an aluminium one? interestingly i got an extension housing for a Falcon (which didnt fit) from Australia and the 3200 one has a roller bearing where the standard BTR one was a bronze sleeve. so maybe they did beef up the gearbox bearing to take the extra load? I have also had the oil seal on the diff go, and that may be down to vibration from the prop. I still have some gentle vibration issues so any one with any suggestions for vibration please bring it on.