99 passat shifting hard 1st to 2nd etc
 

I just brought a 99 passat. Runs good but the tranmission sometimes shift very hard ( sounds like you hit something and it throws you) when it changes from 2nd to 3rd and very minor in 1st to 2nd. 4 years ago the previous owner acidently drained the tranmission fluid and drove it a short period with no fluid. Its a long story. WHen they refilled it the tranmission does this. He's been driving it 4 years like this and it pulls just fine no slipping at all. It does not do it all the time either just sometimes. Any ideas? If I reset the computer would that help any? tramission fluid change and new filter help?