Help! My 2003 Sahara automatic will go into both 4H and 4L, but it likes to jump out of both. I am following operating instructions and the problem is not all the time. Jumps out of 4L on the bumps and when speed/rpms are higher (below 20mph). Jumps out of 4H whenever it wants to. I am learning and new at this. Not afraid to jack it up and try to fix it. Any suggestions?