Today my near perfect 2004 Navigator 4X4 w/143,000 miles started acting up. When I put it in 4 Low and shifted to 2nd (I do this everyday to make descending my steep dirt and rock driveway easier) Nav said it was in 4 Low but it seemed to be in 4High. Raced down the hill. Stopped to take it out of $WD and it seemed to come only halfway out. Front seemed to transfer out but not rear. Took it out on road and it sounded like it was in 4Low yet it was able to move faster than that would have allowed. And speedo said I was doing 80 when I know I wasn't over 25mph. Right now it is stuck in this mode. Tried several times to get it back into normal 2WD but only thing happens is indicator light goes out. Any ideas for this?