1996 Ford Mustang Cuts off when Decelerating

If I start my car and let it idle it runs just fine & when I'm on the interstate it runs fine but the problem is when traffic is slowing down or I come to a stop such as a red light or stop sign it gradually dies down and cuts off. If I give it about 10 seconds it'll start right back up. Only modifications are a K&N air intake, cat back exhaust, & the transmission was rebuilt and the previous owner added a mild shift kit.