It will run fine then suddenly comes to stop.But the brake is off.It's like it's being held back.then it will roll free again

 

Are you talking about the brakes locking up? The car is in neutral and you can not move the car by pushing?

A trans problem such as the trans is in gear, you rev the throttle but the car does not move?

Any noise along with the problem?

Manual or automatic trans?

 

are you you have enough fuel???that would cause the power to stop...