It is probably bad gas... You need to watch what you put in your gas tank, especially around colder weather. When you fill up at a gas station and it's been snowing or raining hard, water could get into the hose itself, and then the next time you pump you've got water in your gas - instant killer of motors! I would throw in some Heet or another fuel addative that helps get rid of water. If it continues to do it, it very well could be something else causing you to studder or stall - possibly even something stuck in the fuel filter and it is not allowing free flowing gasoline from the fuel lines to the motor.
Good luck.