Problem with a Plymouth Breeze..Help

My mom owns a 98' Plymouth Breeze and is having trouble with it. I guess her car starts jumping when going up hills at average speed (25-30) and just in general. She took it to a shop and said there was something wrong with her spark plugs in that the current is jumping or something and thats making the car jerk. It doesnt last long. Maybe a few seconds. I thought it was her transmission slipping in and out. What do you think?