On our recent fishing trip, we stopped at a campground that had uneven grassy sites. I needed to pull one side of the trailer up on 3" of boards to make it level side to side. I put the RL in Drive and tried to slowly ease the trailer up on the blocks. The front wheels just spun in the grass. I then shifted into first and engaged the VTM-4 lock. The trailer when up the blocks with no wheel spin at all. I don't know why the VTM-4 system didn't automatically transfer some torque to the rear wheels in Drive. Any ideas?