Yukon 4wheel controls

I have a 2002 Yukon with the 4 wheel option. I used it twice and the computer brain died. (Pushed the button to go into 4 wheel drive and the light just blinked--no action. Pushed the button to go out of 4 wheel and the proper button came on and the blinking stopped.) Had to purchase a new brain, car was 5k over the warranty. I used this new brain twice and now it is dead after 6 months. Any ideas why?