Any mechanics out there in mylot land?

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I have a ford explorer and on Saturday my SO took it and when I got in it the O/D light was blinking. I asked him if he went four wheeling and he said he had to get through a field so yes. Well the light kept blinking I couldn't get it turn O/D off. It also seemed that it wasn't shifting gears at times when I was driving on the highway after that. Well this morning I get in it and it goes right away no problem. After I dropped my daughter off it wouldn't go forward or reverse. I put it in 2nd and it went until I came to a stop sign and it finally stopped. Well I left it there then I went back a few hours later and it went right into drive and I drove it home. I stopped and put it in park and then put it back in drive and it wouldn't go. Is it the transmission? Any suggestions?