Car turns off

When i come to a stop and take the car out of nuetral quickly my car turns off. Also when im in nuetral and rev the car high then take my foot of throttle quickly the rpms drop really fast after about 3k then it turns off. When i let of slowly or take it out of nuetral slowly it dosnt do it. What seems to be the problem? Could this be valve related? Pls pls help really embarassing problem. Thnx

p.s I have an act 8lb flywheel and an exedy stage 1 clutch with gsr trans.