1989 Mustang 2.3 Liter

It is giving me a real hard time. When its cool out or at night it runs like a dream but when it gets hot out its runs for a short while sputters then stals. I let it sit for all of 5 seconds and its back and running. Im leaning towards it being an Engine Coolant Tempature sensor (ECT) or an Air Charge Tempature sensor (ACT). How far off am I and what else can it be?