Transmission

My car has a slight jerk in it the other day I was on the freeway. I heard my car making a whining noise it sound like my foot was on the gas while it was in park or neutral, but I was driving on the freeway and it was still going. So I pulled over on the shoulder of the freeway and put the car in park and turn the hazardous lights on. I sat there for a second and put the car back in drive and it drove off with no problem, but when I hit twenty miles per hour it did a jerk again. The car has a slight jerk to it when you driving after you hit twenty miles per hour. However, the car still drives all the gears work just fine when you put the car in them. It is just once it hit twenty miles per hour it has a jerk in it and it drives slow when you trying to pull a hill. Does this mean my transmission is going out? Because I do not have any lights on on my dashboard indicating anything is wrong with the car.