I had the same problem when trying to run the X-C at my local track, hard packed clay very dusty and slippery. Seem to have it dialed in pretty good now with the following settings:

Front:
20 weight shock oil (10 is standard)
1 degree toe out
Stiffer front springs (to get a bit of weight transfer to the back)
Proline Edge tyres

Rear:
20 weight shock oil
4 degree toe in rear arm mounts
stock springs
Proline Holeshot tyres
Shock moved to most upright position on shock tower

I got all of this info from the XTM X-C forums at:
http://globalservices.globalhobby.co...wforum.php?f=9