hello, i posted a couple of days agao about having issues with my grand prix, and how i was having problems with the rpms going up and down while the car was in motion. and when the car takes off or is getting ready to shift it seems that the car will make this huge jerk and go, so i had the mechanic look at it and said that it was the transmission in the car, so i replaced the trans with a used trans, but know the car almost at everytime of a take off from a light or a stop will make this huge jerk move before going ahead up the street, does anyone have any clue what this issue is?