2001 blazer 4x4 body is in decent condition the only problem is it has no throttle response above about 2 grand rpms. Before that it ran great and shifted smooth. It has a new fuel pump,Fuel pressure regulator,fuel filter,upper intake gaskets,MAP,TPS, and IAC sensors,plugs,wires,cap and button. Replaced the spider injectors and MAF with used parts. still wont run right

 

Those are all parts you want to try an replace with new. Having said that i did the exact same thing to my blazer 4.3 vortec i'm assuming that's what you have. Might check for bad conection in wiring to pcm witch was my issue. Maybe cracks or breaks in air breather system. Something to consider and i hate to bring up but cam could be ending it's life cycle. Hope that's not the case. Not sure I was much help but good luck to you.

 

Why replace the spider injectors with used ones? They were really only meant to be used once, that's it. I'd start by checking your cylinder pressures and go from there.