My car keeps shutting off while going up hills what could it be?

Hello,

This could be due to fuel starvation. How low was the fuel level when this happened?

If the fuel is very low, as the vehicle travels uphill, this will make it difficult for the fuel pump to properly provide fuel flow to the injectors.
This can lead to the engine shutdown or cut out.

Another possibility is a clogged fuel filter. When the vehicle is going uphill the pump has to work harder to provide enough fuel pressure, especially when the fuel filter is dirty or clogged.

https://www.2carpros.com/articles/how-to-change-a-fuel-filter

Please let me know a little bit more details of what you have been experiencing and the fuel level at those times.
Thank you.