This started a week agoi have a 2007 f550 sometimes when i stop somewhere and i shut the motor off when i get back in it to go it starts up at low rpm and slowly dies like 900 800 700 600rpms then shuts off. i have to leave it for a min then it starts up just fine. I have to check engine light or nothing not smokeing out the exhaust nothing what could be wrong? I just replace my fuel filter so its not them.