2004 Chevy Monte Carlo question

I have 2004 Chevy Monte Carlo never have any problem before, but recently transmition has been acting wierd. For now it only hapends once or twice a week when I drive it. After like 4-5 miles if I stop at the ligth and start going again every time it shifts in to a gear it will jerk. And if I let it sit for couple hours and go again it will stop jerking and it may not happen at all anymore that day or the next day. But it happends when I least expect it. It's been doing this for about five months off and on. Any sugcestions what it could be? Thank you