If your diff was new then its probably been slipping with the grip. Did you bed it in properly or just go out and hammer it? and was you'r slipper set correctly?
I took my x6 round while we were down there building the rostrum and after 10 mins the diff was exactly the same as when I started and there wasn't a speck of sand in the car. The grip levels are just right and the bumps and humps are spot on. I can clear the 4 sleepers in one, no problem
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