bought brand new in 2015, great truck except for this violent front end wobble and steering wheel shaking that has occurred a few times to date but so far only when braking while going down a long hill with a moderate weight in the box. It stops after hitting the flats and things cool down so thought it might be the rotors but they're brand new and shouldn't 'unwarp' if that is it. Rides smooth as glass in all other situations. Tried the different available truck options for brake assist, trailer tow, etc but nothing seemed to make a difference. Chevy dealer checking it out while I'm writing this, but didn't have any ideas before hand other than I'm not the only one who has reported it. Anybody else have this issue with a new truck?