Given that the truck was a lend-lease vehicle sold in Queensland, I'd guess that it was supplied to Australia under the terms of the lend-lease agreement.
Under the terms of the lend lease agreement, it was determined that any equipment supplied by the United States was to be either shipped back to the US or destroyed.
Immediately after the end of hostilities in the second world war, US forces in Australia transferred the bulk of their vehicles, ammunition, aircraft, facilities and weaponry to the Australian Military Forces, rather than ship it back to the United States or attempt to sell it on the global market. (Either of those options would have been a logistical nightmare for the US military!).
This left the Australian Military Forces with a huge amount of surplus equipment which had to be disposed of.
A further clause in the lend-lease agreement stated that under no circumstances was the equipment to be kept on charge by the military forces of the receiving nation (i.e. Australia, in this case) or sold on to other countries. Much of that equipment (even if brand new), therefore had to be assessed as having no value, and was sold as non-commercial scrap. Although the Disposals Commission
wasn't actually wound up until 1959, the bulk of these disposals seem to have occurred between 1945 and 1949.
The records of the disposal process are now held by the National Archives of Australia (NAA). A search of these records using the RecordSearch facility on the the NAA website shows that a number of Army vehicles, including trucks, were indeed sold to he general public, and that most, if not all, of those sales took place between 1945 and 1947.
The records of the sales are now held by the NAA in series MP392/31 - "Lend Lease/US Army surplus vehicles for disposal".
These files are held in Melbourne and contain details including:
prices, vehicle history, indentification [sic], priorities etc.
Unfortunately, I couldn't find any of those records available online, so you would probably have to visit the NAA in person (or hire a researcher) to find further details.