my car started doing this thing in 4th and 5th gear where it will stutter. like, it feels like the engine dies for a fraction of a second and i stop accelerating. Also at the same time i noticed my idle is a bit rougher, like, i can feel the car rumble a little bit whereas before I couldn't. I ran a bottle of seafoam through the gas and for the first 1/2 of the tank, the problem went away then it came back. I replaced the spark plugs and that made the problem go away for about a week and then it came back again. Any ideas? Is the way i'm explaining it too vague?