I have a 4.6 with 136xxx miles on it and the overdrive failed.
I pulled the pan and found what seemed like a normal amount of oil shavings on the magnet, the service plug was still in the bottom so it's never been serviced and the trans fluid is BLACK. I found no metal pieces in the bottom.

WHAT HAPPENED: I would drive normally and the trans would shift pretty hard when going into overdrive, checked fluid and everything seemed fine otherwise. The hard shift continued to get worse and worse until it would shift out of 3rd to shift into overdrive and stay in neutral until i gave it gas and got the rpms up and it would shift into overdrive. That lasted about a few days and it stopped shifting into overdrive all together. I can shut overdrive off and drive normally, but I highway drive often and the high rpms kill the fuel efficiency. Trying to diagnose and fix, any help is appreciated.