Q: 5.7l cuts out when you throttle the engine from a stop. Gets going sometime then hesitates. When it gets to 50 mph it runs fine.

Hi there. Check the IAC (idle air control valve) and see if its functioning. If the engine is having an issue with stumbling, the IAC could be causing the engine to stall out. If the IAC is working properly, then check the MAF (mass air flow sensor) to see if its dirty. A MAF sensor will cause the engine to also stumble when a low speeds if the sensor is malfunctioning. If the engine light is on, then use a scanner to check for any codes to have a starting location for diagnosis. If you need further assistance with your engine cutting out until 50 mph, then seek out a professional, such as one from Your Mechanic, to help you.