Jerking before coming to a complete stop

A couple of weeks ago I noticed just before coming to a complete stop the car jerks/catches a bit, around when the car would be downshifting from second to first gear. The car shifts smoothly when accelerating, and if I let the car roll to a stop without hitting the brakes it does not jerk either.
I figured it was either a front brake problem or a transmission problem. I just dropped the car off to be serviced at a Hyundai dealership, and they just called for me to pick it up cannot tell me what is wrong with it. They said both my front and rear brakes were fine. My transmission fluid was pretty dirty, so I had them flush it. They said the car is not throwing out any transmission error codes during diagnostics, and they said there is no way for them to diagnose what is wrong with it otherwise. So basically they are telling me, "not sure what is wrong. You can come pick up your car that is still broken now. Good luck!"
Any thoughts as to what could be causing this? I am a woman with limited knowledge about cars, and shops often try to take advantage of my lack of knowledge. I want to take it to another shop for a second opinion, but I do not want to sound like an idiot when I do.