4.3 V6 Vortec won't start

Sorry for the lenghty post and misspellings, but I figure the more information I can give the better someone can help me.

,
2002 Chevy Blazer
72,000 miles
4.3 L. Vortec V6
Won't start, turns over but sounds like it is misfiring, (comes to a lurching halt randomly when turing over) OBDII diagnostic code "random misfire in all cylinders"

This happened over night, ran perfect one day, nogo the next.

I have replaced recently,
Cap-Rotor
Ignition Module
Coil
Crank Shaft Position Sensor
Spark Plugs & Wires

I did all this about a month ago, all to absolutely no progress

My wife towed it to a shop & had it diagnosed,(she thought it would be a quick, cheap, fix lol) (I was fishing.... go figure)

They came back with "Spider Injectors & Assembly" (and a estimate of about $2,200) She had it towed back home.

I bought a fuel pressure tester & it was slowly loosing fuel pressure after the key was turned off. (I assumed it was leaking out of the spider assembly somewhere) Also it turns over & sounds correct (no misfire) if you disconnect the spider injector sender unit on top of the intake.

I bought an entire running engine out of a totaled vehicle (everything matches up great & I checked casting numbers to make sure it would be interchangeable)

Last week I took the intakes off & swapped the spider injector sender unit & all of the spider injectors, got it all put back together and I still have the same problem. However it holds fuel pressure after the key is off, (jumps to about 60psi w/ key on, but stays at 50psi overnight w/ key off.) so I guess they were leaking but not the cause of my problem

Today I pulled all of the plugs out, replaced them, disconnected the fuel pump & cleaned out the cylinders from all of the previous cranking, & I was checking spark before I put the plugs back in, I noticed that the #1 cylinder would fire twice on some strokes & only once on other strokes with absolutly no pattern (that I could discern) I checked #4 & it appeared to be fireing correct (once per stroke) I then checked #6 it would fire similar to #1 (twice sometimes) I thought this was wierd so I swapped the coil & ignition module w/ the ones from my other engine (again) & had the same result, I figured it was some wierd vortec stuff I proceeded with putting it back together. With no fuel connected I tried to spray carb cleaner in the intake while turing it over it still would not start, sounded like it wanted to a few times, tried it with the air cleaner (mass air flow etc..) hooked up & with out, same result.

Like I said I have an entire engine sitting in my garage, but I don't know what direction to go,

I am pulling my hair out over this one, can anybody give me some advice.

Thank You for your time,
Cody Samford

Cody, Have you ruled out the ECM? I believe it sends the signal to the moduale. Not sure what colour wire to test, a manual would tell. I have a posting for a vortec no start with a TBI. I'm leaning that way on mine.
Cheers Stewart

I finally got it fixed, it turned out to be the distributor, after all of that, It may have been the cam shaft position sensor, which is attached to the distributor, All I know is that after sticking a new one in, it fired right up after sitting for almost 6 months, I still don't know how it went out overnight, however it was freezing when it went out, maybe the cold??? I was getting fire but it was "double sparking" etc... as I stated before, really weird, but I am super happy to have it fixed.

NOTE: CHECK DISTRIBUTOR IF YOR SPARK LOOKS ERRATIC

Thanks, this board is great I have been reading quite a bit since joining