OK, my bad! I made an assumption that I did a third drive cup... but after running round and getting the last one in sydney, and stripping the bad girl down only to find the diff fine! Stupid me didn't even inspect the truck, it was the pin in the hub that has the two e clips to hold it in, part #GS277 (she's STUCK in the barrel!) . Now I'm up early to go and get a pin and e clip set to run the beast this weekend.
Aaargh!!!