Hello, I'm new to the group.

I had a question that nobody I know seems to have an answer to.
I have a 1997 F150 5.4L 4x4 and recently I got into my truck to drive and when I put the gear selector in reverse it started clunking/grinding but when I put it in drive everything was normal. Later that day I got back into my truck and when I put it in drive and stepped on the gas it didn't go anywhere, it just acted like it was in neutral, so I put it back in park and back in drive several times for it to actually go into drive. When i started to drive, it wouldn't go out of first gear the whole ride home, which was about 2 miles. When I finally got home and put it in park it started clunking until I shut the engine off. I thought it was just in need of a rebuild because i didn't know when the last time it was rebuilt and my truck has 277000 miles on it and all the fluids were good. So I pulled the transmission and started the teardown process because I was going to rebuild it and it looked as if it was recently rebuilt. All the friction washers were fine and the bearings looked good. There was no metal in the pan, just a little bit of gunk built up around the magnet. So now I'm stuck. Can anyone help me? Thank you