Egine starts then slowly dies

SOURCE: when you start the truck

It sounds like a weak fuel pump. You would need to have a pressure gauge to hook up to the exit end of the fuel pump to test the pressure. A call to a tech at a local dealer could give you what the proper pressure should be. I'm thinking it should be 35-40 lbs. If the pump is weak it may have enough gas to get started, but as it runs, the pressure bleeds off, so it doesn't send enough fuel to the engine causing it to die. If you push the accelerator, basically the same thing happens, it tries to jump up the pressure and can't keep up. If you don't have the proper tools or gauge to do this, it should be examined by a mechanic.