Good thoughts, thanks for them...
I just checked for engine codes with the old "paperclip on ALDL A and B terms" trick. Nothing noted- just 12 over and over.
I am going to go ahead and fabricate new positive cables from battery to starter, and battery to alternator, simply because the OEM stuff is looking rather ratty, and I also added a fan assembly with 75-Amp inrush, 40-Amp steady ratings. Granted, it's actuated by relays and runs off a piece of 8 gauge to the battery, but the battery (and thus the rest of the truck) is still supplied by a suspect looking piece of 10 gauge. At any rate it absolutely will not hurt.
I am also going to make new grounds- firewall/body to block, block to bussbar, frame to bussbar, bussbar to battery. I will be making these of 2-GA welding cable, hammercrimped and soldered with marine grade heatshrink to seal them. I don't expect this to be a magic bullet, but I do think it will be part of it.
The reason the parts were replaced is- to get the engine running. It came to me without a distributor, and I pulled the TB off the 4.3 and put it on the 5.7 (and to recap, yes I did install the proper injectors, and I also replaced all the gaskets and FPR in the vicinity while I did it. The distributor was broken on the new motor (motor was running strong in the junkyard truck I drove it in, I damaged the dizzy in lashing down the motor for transpo).
Fuel pump was replaced as it was suspect after I've driven the truck for 20 years without touching it, and the vehicle was deadlined at the time. I used a Delphi unit, as it has a good reputation for quality. I get your point about even new parts being possibly bad, though.
Ignition module was tested at the parts store on their tester. At the time it was suspect (when I started having this problem). I tested it 10 times, it failed the last 8 (always warm up parts when testing out of position, as heat is the enemy of electronics). It failed High-RPM output and SPOUT each time. It was a warranty replacement.
Coil was replaced, as I'd been running an old 1992-vintage Accel Supercoil. It had seen service in a couple Jeeps, a couple Fieros, and the Blazer for the last 20 years. It was questionable at the time according to my readings (which I now question, as the meter smoked on me shortly thereafter) so I splurged the $15 for a new OEM one. Coil may still be the issue, if my grounds are aas questionable as I suspect- I have yet to run a ground strap from it's new home to the block. That will change soonest. Tonight, if it's not raining.
Plug wires were chafing to the core, so replaced with fabricated units. I've rung them out good (IIRC, 50 ohms) but will re-ring at some point, likely the weekend. St the same time I'll read the plugs.
You said "datalog for trims "... might as well be speaking Greek to me. I'm VERY new to this- if I log the data can I upload it so you can look over it and advise? I don't expect you to spoonfeed me, but a nudge in the right direction would be much appreciated.
EDIT to add: the coil harness is new- I fabricated it myself with connectors bought at Oreilly. That's nothing meant to impress- it's simple work. But I did twist the wires from the ignition module 2-wire harness to the coil (prevents crosstalk and inductive-coupling, and doesn't cause issues). Everything was soldered and heatshrunk. Yes I used electrical solder, not plumbing- the difference being mainly in the rosin flux instead of acid flux (I've done lots of soldering work on DoD equipment and high-end autosound and security work, so my connections aren't the problem, guarantee 100%). I taped and loomed the new harness, and it was built long enough to where it's not tugging away from the connections- in short, there is no way the harness I built is the problem).
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