Thats a very common surface. I can't tell you anything about different adjustments on your buggy because I don't have any experience with it but if you have free time just look at how all of your linkages work and where there setup. Even change them (especially roll center) and see the difference that they make. More roll center will give you more negative camber roll as the suspension is compressed and gives you less of a tire contact on flat ground but more contact if your going into a berm where you need that tire to have as much contact with the berm as possible. Its something easy to test just on your work bench by putting the buggy on something flat and just seeing how your tire contacts the table with the suspension in different positions. Also lighter rear shock oil, ligher rear springs, or less anti-squat will give you more rear bite by transering more weight to the rear tires but you should really make sure your alignment and roll center is in the right places first.

Diff settings and run you in circles especially the rear because the rear is going to react different ways on throttle when you change the center diff. I'll try to find a post that I explained how the front, center, and rear diffs worked with different weight oils. If I find it I'll post it on here. Eitherway it sounds like your rear diff oil is to thin.... it always makes the rear of a buggy just feel like its swinging in the wind. I'm running 3k in rear and its doing great.