Seems like you have a C6 trans so the trans is not the problem.
Is there not an emissions label under the hood with a vacuum diagram?
Is this truck fuel injected or carb? If carb you could probably block off all vacuum pipes, except the one to the trans and one to the distributer (if there is one).
It sounds like the extra load on the engine when you shift to Drive is causing it to stall which could well be a vacuum leak problem (if carb motor) or ignition timing or carb choke problem.