With lots of kilometers in the edaien of sahara I would say:
The most important single upgrade in sand are tires - tall with a good sidewall ... 7,5R16 or 255/85R16, Mud terrain last longer e.g. BFG KM3. Those you can deflate to 0,8 to 1 bar (11-14 psi ;-) without damage
Second is suspension...