Shuts off when transmission is shifted into gear?

This can be many different things, from a vacuum leak to a locked up torque converter, we will need more information to help you. Please go over this guide to help.

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

If you upload a short video of the engine when it stalls I can tell much better and guide to the problem without needless inspections/repairs.