when I shift to reverse or drive engine will stop / shut off?

Hello,

I have seen the torque converter clutch solenoid stick on causing the problem you are describing but to be sure can you upload a short video of what the van is doing?

Here is a guide that can help you:

https://www.2carpros.com/articles/stall-at-idle

I have also seen a dirty throttle body, or a vacuum leak cause the problem as well.

https://www.2carpros.com/articles/throttle-actuator-service

This guide is used when the engine is cold only:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Please go over these guides and report back.