Cheers for the advice Jim.
If Im honest, I would have to say that I just dont know if the diffs are too loose.
I have followed the manual to the letter (i.e. tighten up diffs, then loosen by 90 degrees) and then I went with one of Grant Williams astro setup sheets for oil weight, shock positions, etc.
The only thing I could say is that the diffs are maybe a little "raspy" when you rotate them in your fingers. I use Nuclear diff grease and its good stuff, but maybe my balls are shot (ohh matron) - would that make a different to the handling on astro? Like I said- seems much better on the clay/dirt.
Thanks for the help