transmission issues ???

1999 GA .3.4 auto. 100,000 miles. car at operating temp. put car in reverse back up then put in drive. Car seems to rev up and move ahead slowly. put car in neutral then back in drive and car is fine. only does this occassionly. Any ideas??

Does it slip when turning left or right?
I'd have the fluid level and condition checked, sounds like its low.

It is about the interval time to change the fluid & filter.