Seems odd...while I brake to reach a stop light, sometimes the car jerks while my foot is on the brake. It seems like the jerk iswhen the transmission is shifting down from 3rd to 2nd and 2nd to 1st...not sure though...What could this be?

 

if its shacking or veering to the side while brakingthen its most likely your
brake rotors.
had it happen in my other car.

 

What should I do replace them or have them turned? Does this have anything to do with Brake Assist?

 

It has nothing to do with brake assist. brake assist is only used in emergency braking conditions. i would check the the trans fluid level. if it happens when the car down shifts it could have something to do with the trans. you could find a side street and start braking and manually down shift to see if it could be the trans.

 

The front rotors are bad and I don't believe you can turn them, you just have to replace them and it is also better to change the pads, too. Check on the rear rotors, too.

 

possible transmount or motor mounts