Well, truck runs and drives, FINALLY. What an arduous road.

The truck would go through phases where it would fire right up and run great, or not fire at all. I thought it was a pcm connection issue. Tried a different pcm and it both ran and did not run with the new pcm.

Made sure my grounds were up to snuff.
Batt to frame,
batt to engine
engine to fender
pcm grounds to fender (about 12" away from the other engine to fender ground. Both connected to same steel bracket)
starter to frame
plus all the black and black/white ring terminal wires.

So then I checked the fuel pressure. 60psi when cranking, 53 psi for a 10 minutes after that when I pulled the gauge off. So my hypothesis that maybe my injectors were bleeding down into cylinders was shot. Changed FPR anyways.

It still wouldn't start after changing the FPR. Checked a plug, and it was soaked, of course. About 10 minutes later I tried the key and it fired right up! There goes my "its too flooded" hypothesis for why it wasn't starting at times. It started very well for about 4 or 5 days after that. Continued reassembly and went to pull it out of the garage to work on a different project, wouldn't start. \

We fooled around with it the next week and it was running well again. I went to take it for a test drive and it died half a block away. The pedal wasn't responding and at times wiggling the pedal or the wires would help, so I replaced the pedal and harness going to the pedal. Wouldnt start at all. By this point I was missing my exhuast appointment.

Back to google I went. Most of the 'no start 5.3' hits on google are related to not cranking over, rather than cranking over and not firing. I found one post, ONE mention, that the pcm grounds should go to the head (mine go to fender remember, and there is a fender to engine groud 12" away...). What have I got to lose though. So I hook booster cables to both the pcm body and the pcm ground bolt and stick them on the head. ...and it fired right up like nothing was ever wrong.

So when we say these engines are picky about their grounds, we MEAN it.

So I unloaded the bed (full of junk from the swap), changed oil again, and hit the road. Drove 130km at 115km/h, no problem.

Questions:

My fuel gauge doesn't work. I read that the fuel gauges are grounded through the pcms on these trucks, so I found the ground wire for it and grounded it. Now it just dances from 3/4 to above full. I believe the fuel gauge was working in the truck previous to the swap.

VSS: I have my purple VSS (VSS high) wire. It is a twisted purple and green wire with foil in an extra sheath around it. It is going to both the VSS wire in the 5.3's C100 and the speedo in the 98. This must not be right? I don't have the diagrams in front of me otherwise I would be more specific.
Is the VSS wire in the 5.3's C100 an input (from the VSS) or just an output (for the speedo)?

I haven't looked into getting my 4x4 working yet. Is there a signal from the pcm to the front actuator? Or should it just work based on the old 98's harness?

I'm mostly confused about the VSS, because I thought I had done it right based on what I had read here. Any help on these matters is greatly appreciated!

The truck sounds great with the FloPro V Force dual chamber muffler. It is dual 2.25 in and a factory 454 truck 3" tailpipe.