Check the cable that runs from the push pull button on the shifter that goes down through the floor underneath the truck. I had mine separate under the truck that was allowing the whole thing to move instead of just the inner wire of the cable. I bent up a special piece of metal with a series of clamps on it to hold the outer jacket of the cable in place. Works perfectly and has shifted this way for years now. Mine would shift into high but would not go back into low without crawling underneath and holding the outer sheath and moving the inner wire on the shift cable. Hard to describe and it took a while for me to find exactly what was going on but I fixed the problem with the new bracket and hold down clips.