When I slow down my car dies. It starts back up right away. What is wrong ?

Sounds like a faulty contact , but where that is , would need to be diagnosed with proper equipment , how consistently does this happen?

Just started after I had new battery put in yesterday

Aha! Always more to the story. That info changes the picture completely, I suspect that a 'memory saver' was not used during the battery exchange, thereby resetting the cars computer. That clears the 'learned' idle and other values. Try googling your year and model and engine , for proper 'idle learn procedure' or as in many cases I've seen , first start of the day , next time , with ALL lights and accessories OFF , start it and let it idle for 10 minutes , see if that helps.