2014 Sienna SE vibrates when braking

Just noticed my 2014 Sienna SE vibrates so bad when going down the hill. Does anyone have this issue? My brakes and rotors were bought from Toyota dealer and replaced about 20k miles ago. Quick google search people said that possibly the rotors were warps due to the heats. Also due to the lower clearance of the SE there are not enough or airflow into the wheels to cool it down. Anyone experienced with this issue with their Sienna?