2001 kia sophia

I have a 2001 kia sohia, the tranny slips when trying to accel from drive. You can put it in low and manually shift it. Once back in drive and going down the highway, the tranny will shift up and down normally with only a slight slip when accellerating very quickly. Once you slow down and stop, its back to manual shifting. I've changed the fluid and filter and it still does the same. Does anyone have any ideas or can supply any links that will help out. Thanks