Engine stalls while driving on highway.

The check engine light indicates that the computer has detected a malfunction in the engine/emission control system and has diagnostic codes and data stored which would be essential in diagnosing the problem. A technician with a scanner could access the diagnostic codes and data and then be able to give you a diagnosis. If you want to find a specialist, here's a directory link for you: https://repairpal.com/buick-repair-in-new-braunfels-texas