automatic gearbox oil?

hi.

i bougth a 95 modell audi a6 2.5tdi with auto box, and when i changed oil and filter, i found out that they had used dextron 3 oil, instead of the vag original auto trans fluid, how bad would this be for the box?
the oil didn`t smell burned, and it looked ok.
but, sometimes when i drive normal, it shifts pretty hard.
changed the oil about 2 months ago, would it be of any use to change the oil and filter one more time to get everything out?

thanks