The steel in the rear leaf springs suddenly broke in half (under no load). it happened twice - in the left rear leaf springs in ~2016 (~3 years of age), and again in the right rear leaf springs last week (2018). this is not even a mechanical device - just a passive heavy gauge piece of steel. the vehicle is very light use, and in both cases there was no payload in the flatbed. gm appears to be using a substandard grade of steel in critical areas of the vehicle. the rear of the vehicle dropped when the springs broke, and i consider this a safety problem if driving at high speed. in addition, the steel rod that connects the inner driver door handle to the door lock, also snapped (so you can not exit the vehicle from inside controls). it appears that gm is using a cheap substandard grade of steel in their vehicles. estimated date of first event below. *js