Truck starts but shuts off immediately

My truck starts fine, but shuts off. If I keep my foot on the gas it will run. I can let it out all the way down to what the normal idle is and it stays running, but as soon as I let off it shuts off. After five to ten minutes it will finally start idling on its own and everything runs fine. Even if I stop, turn off the engine, and start after being in a store while running errands it has been fine, but if it sets for a few hours I have to force it to run until it starts working again. The truck has hesitated or dropped rpm's a few times in the past, but never shut off. This started a week ago and is taking longer to start idling on its own each time I have to go somewhere.