2008 Buick Enclave engine problems

Tl* the contact owned a 2008 buick enclave. The contact stated while driving at approximately 70 MPH, the vehicle unexpectedly made an abnormal low gear noise. The contact was alerted that her vehicle was emitting fire from underneath the vehicle, she immediately pulled over and noticed a cloud of black smoke, within a few seconds later the vehicle engulfed in flames. The vehicle was put out by the fire department and a police report was taken. The contact sustained smoke inhalation but was not hospitalized.

While driving the vehicle just shuts down. The first time it restarted, but on the second occurrence it would not restart. The vehicle has "stalled out" several times while traveling at rates anywhere from 25 MPH to 45 MPH. We have had it towed to the shop (including the dealer) 3 times and are told nothing is wrong. But the problem happened again today. I see other people are experiencing the same problem. Although we have avoided it thus far, it is going to cause an accident.