Engine Stall problems of the 2007 GMC Envoy

Engine stalled while driving down an incline without any indication until applying the brakes to find the power brakes had been lost. Weather conditions were slick and the vehicle started to spin and could not be corrected due to loss of power steering. Vehicle could not be slowed using the lower engine gears. Once the vehicle coasted to a stop, the battery light came on. The vehicle was put in park, turned the key to the engine-off position and then on. Onstar diagnostics did not detect any problems in system tests. Fuel level was approx. 3 gallons. ************************************************************************************************** failure almost caused an accident of running over a pedestrian and collision with other vehicles (no control and no warning from the vehicle systems of stall). This is the second incident; initial incident occurred while leaving inclined driveway - potential of entering roadway. My child was riding as a passenger in the vehicle for both incidents. ***************************************************************************************************.