98 Lesabre just turns off

I have a 98 Lesabre and when driving it just shuts off. I cleaned the corrosion from the positive battery connection. I even cut open the red boot and cleaned between two of the three connections. The connection to the battery is tight. When drivind it just turns off as if the battery gets unplugged. I have noticed in the past that when I start the car the alternator gage is low for about 4 seconds then jumps right up to right before the red mark. After it dies it will start right up no problem.

Any ideas would be helpfull.

Thanks