1997 K1500 5.7 Vortec will turn over but will not start????

[love2heargobble]

I have a 5.7 Vortec that runs like a new one when it runs; however at times when I need it puts me down. You might go out a couple days later and she starts? This has been going on for about year and a half. I mainly just use it around my farm because I'm scared she will leave me stranded. I have replaced disturber, plugs, wires, ignition coil, cam sensor, crank sensor, fuel pump(twice) fuel filter, check fuel pressure(good), just last week changed the spider injector assembly(which I thought fixed it only to find out several days later after driving it my demon has came back!), I then replace the timing chain and gears(again started good and I thought I fixed my problem finally! Only to go out this morning and she wouldn't fire. After I turn key off she acts like its trying to fire but wont? Any help? What else could it be??? Computer? something on top end of motor? Like I said it runs great when it will start.

Thanks