98 aw4 reverse problem
 

Ok so I left work and I put my jeep in reverse and it worked great. I park in gravel and when I backed up it spun the tires over. I drive home far lunch and let sit in my yard far 15 minutes and now it barely moves in reverse. I put it in forward and it will roll the tires over in Gras but not reverse. What can I look at. Where do I need to start looking...