96 yukon extended crank

Hello everybody I'm new to this post I have a 1996 GMC Yukon I let it sit for 2 days I've replaced the fuel pump, filter,even bought a second generation spider injector system for it.yet I still have a hard time getting it to fire up 1st shot I'm confused at what could be the problem.i have exhausted all my options with it. The new injection system came with a brand new f.p.r.on it as well. I have.changed the plugs, wires, dizzy cap and rotor button. Any suggestions on this issue? Thank u in advance..