Slipping transmission in an old Auto ?

Hi guys,

Recently my gf's old 1990 Civic hatch has been playing up a bit, the gear changes sound quieter, ( It's an Automatic ) but if you drive it around rather abruptly, if you put it into park, the engine starts getting louder and louder with higher RPM's. Feels as if you putting ur foot down on the accelerator. Is this because the transmission still think's it is in Drive ?

Does this mean the tranmission is screwed, is it very expensive to fix ?

If it is, she's gonna wait for a bit, and look at getting a new civic. Thanks

I dont know much about car engines, but it could be the timing belt

does the tranny slip at all? falir up around corners.

could just be carby problems