Car keep cutting off

Is the Check engine light on? Any noises or other symptoms?

I don't know your situation but in some cars when the computer detects a serious problem that could cause the catalytic converter to fail, the computer will put your engine into 'limp mode'. That's where your engine will only produce enough power to get you to a place to get it fixed. You'll give it foot to the floor but only go about 30 mph.