Ok I don't want to insult you, but maybe it's so obvious that it's been overlooked - have you double-checked the firing order?

If there is spark on all 8, and fuel to all 8, but only 4 are making an explosion, there's either a compression/leakdown or a timing (injection or spark) issue.

Have you done a leakdown test? I know you've got good compression, but these motors are known for cracking between the valves. Typically it's not a big problem though.

I had a 5.9 Dakota that the dealer fixed the plenum gasket under warranty, then I fixed it again about 10k miles later with the Hughes kit because it failed. After I sold it, the new owner didn't take care of a leaky exhaust gasket and wound up blowing the head gasket at about 100k. When I pulled the heads off, 6 of the 8 cylinders had cracks between the valves.

 

you seems swapped out everything to exclude the problem, do the basic thing, check firing order of each plug wire, and make sure every injector connector has pulse. that is all. i am not an A tech but also ase certified in engine performance and electronics for 15years.

 

It's the PCM as previously stated..

 

How good of spark at your getting at the plugs?

 

PCM was replaced 2 days ago with no change.

 

It was my #1 check. It came to me with new cap/rotor/wires so I verified #1 and firing order in clockwise direction on the cap. All 8 plugs and injectors are firing with good compression. It really doesn't make any sense.

 

No, it doesn't. You apparently have everything you should..... so, why no fire? I almost think it's time for an O-scope, and see what things look like. (spark energy, and injector pulse....)

 

a good/smooth runing engine must has compression, spark, fuel, and timing. you got everything. don't trust thoes ignition caps, i seen one go bad for gm V8 new. just do the double check on firing order and swap with a new cap, it happens.

 

It's never too early to haul out the o-scope to check waveforms and synchronization.

 

im not a certifided tech or whatever but if ur injectors are working and you got spark... and no fire ... i would think your intake valves on those cylinders arnt opening, they probly have good springs but bad push rods lifters or worn cam... just my thought