If it drove better when you first bought it, then something may have gone wrong. I'm assuming its still new and you are covered by warranty... so you should take it back to the dealership to be looked over. Explain your problems and let the technician diagnose it for you.
I own a 1998 Jeep Grand Cherokee Laredo with 5.2l V8, I burn regular (octane rating 88) in it. Problems with stalling could be linked to poor fuel, try adding fuel stabilizer and topping up with fresh gasoline. Other problems may include an old fuel filter or clogged injectors. A good service...