2005 ford expedition Eddie bauer

Driving up a hill, when all of sudden it was like I was in
neutral, but I wasnt I was in drive. I pulled over put in park,
then put in drive in started moving again then nothing like it
was in neutral. Pulled over put in 2nd drove to top of hill to
rest area. Stopped put in drive again it drove but seem
would stop when putting on speed. Drove a ways on 2nd
the called tow truck. But while waiting for two I'd put in
drive and it would only drive while going at slow speed.
What could this be??  All other gears worked. When two
truck took by car off his truck I used drive to park it in my
parking lot.