Intermittent stalls in traffic

My Lexus stalls suddenly in traffic while I am slowing down. I’ve had the fuel injection system cleaned about 8 weeks ago as this seemed to start after apparently getting a bad tank of gas and was further aggravated by fuel line cleaner. I don’t even have to put the brake on. The RPMs drop to 0 and the car stalls. When I took it to the dealership, they were unable to duplicate the problem. After the fuel injection line was cleaned, the car was fine for a few weeks. Now it is just as bad and happens at least a few times every time I drive the car.