Why does vehicle cut off when driving?

It sounds as if you may have an intermittent throttle switch fault. It is part of the idle speed control motor. If it does not acknowledge that the throttle is not at rest, it thinks it should still be in control of idle speed. As you accelerate, the pcm sees the engine speed increase, but due to false info it thinks that the throttle is closed, so it retracts the speed control motor shaft in attempt to lower the suspect high idle. When you let off the gas to coast or stop, the throttle plate slams shut cutting off air and resulting in stall.