I have a 1999 5.2 1500 4x4 when it frist starts if you let your foot of the gas all the way the truck shuts off. After the truck warms up its fine. Acts like its running out of fuel does not have a fuel filter 1 unit in tank i think.

 

Its sounds like there is a problem with you IAC (Idle air control) valve. It is known for going to hell. It is located on the back of the throttle body which is on top of the intake manifold

 

+1

 

Deffinetly sounds like the idle air controller. You could try just cleaning it up with carb cleaner, but it's probably shot. You can get one at any autoparts store, but I've heard alot of problems with ones from autozone, so you might want to avoid that one.