Truck shuts off when I gas it. Stays on when idling. Any ideas what it is?

Hello, My money is on a bad in-tank or mechanical fuel pump. If one is working, the engine can idle, but once you demand more, there is little that can be done with only one pump working. Fuel lines, fuel filter, fuel pump fuse, mechanical pump inspection (for metal shavings), and water separator need to be checked. Let me know any questions you have, and here is a link if you would like shop recommendations: http://repairpal.com/ford-within-10-miles-of-chinle-arizona-86503