I just recently bought a 99 Grand Cherokee from a private seller after having my car totalled in an accident. Of course the woman told me there was nothing wrong with it, she just wanted to buy something nicer... and apparently she was lying. Since the day after I brought it home it has been shutting off on me while driving, while sitting in park, and while sitting stopped at a light or in traffic. It seems to idle a little rough, but other than that I havent really noticed anything. It doesn't give any warning or making any odd noises, it just instantly shuts off. At first it would only do it while I was sitting stopped at a light or in my driveway, and it would crank right back up. But now its gotten to where it does it even while driving down the road, and it takes it a while before it will start back up for me. It also now will sort of slip while Im driving. It will lose power and the RPM will gradually go down, but if I rev the engine it will catch and the RPM will jump back up to normal. Other times it just drops straight to 0 and dies. Earlier today is the first time Ive gotten in it to go somewhere and it didn't crank right up, it took about 10 minutes for it to start. It has brand new spark plugs, oil change a month ago, and my boyfriend just put a brand new fuel pump in it last week. Also had the fuel injectors tested and they are fine. What could cause this??