I have a 1997 f150 5.4L 4x4 and recently I got in it to drive and when I put it into reverse and as i was backing up it was grinding. When I got back in it later, I went to put it in drive and it wouldn't shift. I had to switch from park and drive around 20 times till it eventually went into gear. When I was driving it home it wouldn't shift out of first gear, and then when I got home and put it in park it was grinding. So I pulled the transmission and tore it down and I didn't see any damage. The fluid was still good. All the friction washers were good. There were a couple of small bearings that were a little darker but nothing that would've cause what it was doing. There wasn't anything in the pan. So my question is what could the problem be?