Transmission shifts hard from first to second gear

Two weeks ago I put my car in reverse and it did not move, then there was bang and the car jumped into reverse and the engine light came on. The car drove a little sluggish for a few minutes. And then drove fine until yesterday. On yesterday morning after driving my daughter to daycare I was preparing to back into parking space and it had a bad transmission fluid leak that I had not noticed. I checked the level int the afternoon and it is was barely any on the stick. I poured a quart in before I left for home and it was driving sluggish and there was a noticeable whine but not knocking when shifting. Once I got home I found that the leak was coming from the filter so I replaced it and added fluid. This morning it shifted into reverse fine, but now when it shifts from first to second there is a bang with a jerk and after that the rest of the gears shift fine. When it downshifts from second to first there is a slight jerk that is barely noticeable. After getting to work I put some Lucas in there and drove around but it is still doing it.