My 2002 mercury sable is constantly shutting off while driving.

What is your question?

For the past few weeks while driving the car is shuts off suddenly. While stopped at traffic lights the car bucks as if it's trying to shut off. While driving uphill it looses power. The other day while going uphill it lost power (wouldn't go up the hill) and just shut off. Not all the time but at times when I turn the car on I get a faint smell of gas. I'd like to add that until about 5 days ago, it would remain running in idle, now if I have it running in idle in the driveway after about 5 minutes the car shuts down. It always starts back up when it shuts down (although sometimes it sounds like it refuses to restart). At the onset of these problems, I assumed there might have been water in the gas tank so, I did put some fuel injector cleaner in before putting more gas in the tank. Needless to say my assumptions proved wrong.