3400, V6 engine, my BCM keeps going out, what would make it go out in 5 minutes

I can replace the bcm, and go thru the process for the security light with the ign. Switch and it all sets up then after startin a time or two the bcm goes back like it was, all lights on dash and gauges come on for 3 seconds then go out and the tach and speedometer do not work. Can turn key on and jump across starter, it starts and runs and shifts fine, but no gauges or warning lights.