Will not go over 30 MPH and intermittently shuts off while driving?

Hello,

It sounds like the vehicle might be in limp mode/reduced power mode.
When a vehicle goes to limp mode it will have low power and many times it will not let you go faster than a certain speed. It is a safety feature for protecting vehicle's major components.
A vehicle can go to limp mode for various reasons. Usually for an issue with the engine or transmission control module.

https://www.2carpros.com/articles/engine-has-low-power-output

Typically the engine light gets illuminated with the limp mode.
If your check engine light on?
If so you would need to retrieve the code(s).

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Scanning for the code will help determine what could be reason for the vehicle to have this issue.

Please let me know of any questions.
Thank you.