Sport mode stalls engine?

Sometimes when I put my car to sport mode and I push the gas it goes to 4th gear or 5th. when I take my foot off the gas or break it stalls on 4th and it still makes the loud engine noise as it I was still pushing the gas, only when I'm really slowing down and only going 15-30 mph. I have to literally break completely to pretty much stopping the car still barely moving so it goes down to normal gear.