I've got a 1994 GMC Jimmy 4.3 vortec v6. The truck starts fine. It idles rough, and would occasionally die, at a red light for example. I replaced the fuel pump, plugs and wires, and the ERG valve, as it was throwing a code for it. Now when accelerating it stalls and hiccups, especially when going up hill slowly. At first if I opened up the throttle, like driving 70 on the freeway, I could drive it, but now it's much worse. I don't even think I can get it out of my neighborhood. 
You may also want to check inline fuel filters they may need replacing
SOURCE: Starts fine, Idles fine, Drives Fine for a while
you might want to chk. the crank sensor and or cam sensor. sounds more to me that it could be fuel problem. chk. fuel pressure. pump could be on its way out. don't be fooled by hearing the pump running as they sound like they are pumping but there not, at least not enought pressure to keep it running. pressure should be around 50 p.s.i.
SOURCE: 1994 GMC Jimmy hard to start and runs rough when first started
did you do a fuel pressure test? if you havent do it its cheep an at least you can elimanate that. if thats not an issue, then there is only two other things crank sensor, and if there is one cam sensor.
SOURCE: 1994 GMC Jimmy engine runs rough when cold; smooths out when warm
you need to have the codes checked to know what direction to start repairs,Autozone does this for free
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