Whenever we stop or slow down, the car stops

Welcome to 2CarPros.

The idle issue can be related to an engine vacuum leak, a faulty idle air control valve, and so on. Since the head was replaced, my first suspect would be a vacuum leak.

Now I'm not sure exactly what is happening. Does the starter engage? If it does, have you checked for spark and fuel to the engine? If it doesn't crank, have you checked the starter relay and fuses?

If the starter does engage, take a look through this link to see if anything is helpful.

https://www.2carpros.com/articles/car-cranks-but-wont-start

Let me know exactly what is happening. From what I read, it sounds like the starter engaged and by itself, stopped working.

I will watch for your reply.

Joe