vortec 4.3 motors have a lot of fuel related issues. They are very picky when it comes to fuel pressure. I think the earlier years were worse with the central injector. I hear a lot of people recommend taking the throttle body off and look down into the intake with a flashlight to see if there is fuel leaking out of the injector unit or the hoses under there. A fuel leak in there can keep them from running correctly or at all. Do some searches on s10forum.com and see what you can find. Sorry I cant be more specific. I dont have a vortec myself so Im just going off of what I overhear from my s10 friends.
