Could be a few things. Put a fuel pressure gauge on it and watch fuel pressure while its running. Drive it. As soon as it begins to sputter, take a look at the gauge and see what the fuel pressure it. Normally, the pressure should be a constant, no matter what the truck is doing. If its junping up and down, you have a fual related problem. If the pressure stays strong even after it stalls, your fuel system is alright. From there if the pressure checks out, the next thing I would be looking at would be ignition. Before that though, check fuel pressure first and make sure its at spec.