transmission troubles

my aunt has a 89 bronco II it has the 2.9 fuel injection,4 speed auto,the other day she was going home it just stopped pulling so she pulled over checked the fluid it was low,so she filled it up and it pulled for awhile then stopped again,now it only pulls in 1st and 2nd gear it wont change to drive and it wont move in reverse either,they changed the filter and new fluid that didnt help at all anyone know what could be wrong? thx for any anwers.