I had the best luck running 30k, 125k, 10k front to rear in the diffs.
I wrote the guide over on rcshortcourse.com on the D8 shock instal, it is complete with shock locations and fluids to use.
The slash 4x4 has some special things to watch for too. The driveshafts MUST be free from binding(the slider portion), or they will interfere with the suspension action. The bearings are also notorious for going out in short order, keep an eye on them for binding. Also, make sure the suspension arms move freely on the hingepins.