I was messing with my IP on the '94 and afterward the truck stalled in 5 seconds of run time, DTC for crank sensor only. I cleaned it's connector, as has worked in the past, but the crank sensonr code is the only one that comes up, engine on or off, and it will stall, except if I unplug the optical, it runs in limp.

I was wondering if something other than the CPS could cause this? I am going to switch it later today on warranty (1 year old) but I'm still wondering how messing with the pump could precipitate the CPS failure or is it pure coincidence? If the CPS is bad, how does it run in limp?

If the truck runs in limp mode, with the optic sensor unplugged, then the ECM is relying completely on the CPS sensor so it must be functioning.
Thats a good question QM, let us know what happens with the new crank trigger.

You've made me think it is something else. Is there a limp mode that runs on the optical only as well. I'm thinking about unplugging the CPS and seeing what happens.
I could read all the Optical data ( timing, angle, fuel temp) and I saw the crank sensor counting cam pulses 1...2...3 then it stalls.

I don't want to say what I did, but by all rights I should be switching the IP for my backup, I just wondered why it was the CPS and not the IP that threw the code.

I could read all the Optical data ( timing, angle, fuel temp) and I saw the crank sensor counting cam pulses 1...2...3 then it stalls.Yes, limp mode can run either way, missing CPS or Optic LO RES signal, but not both.
If you were reading CAM PULSE error counts, then you are not getting a signal from the optic sensor.

How hard is it to take the head off a DS-4? I was thinking about putting the 5068 back on with the 5288 head.

3 bolts, and 2 nuts for the wiring harness, and you'll want to remove the PMD too.
You just need a good way to hold the pump still, like in a vice, with the head sitting up. Remove the 3/4" bolt on the PMD side, the 3/16" allen head bolt on the Stepper motor side, and another 3/16 on the bottom. You'll want to give the 3/16" ones a good rap or two with a ball peen hammer or you'll break your bit trying to get them out.
once those are out use a 9/16 wrench to free the head up rotating it side to side and just pull it out.

Cool! I could put my ebay 5521 on but I'd rather have the 5068 in there.

To do it the 'right' way, you should send both cores in and have the 5521 built with the 5068 cam.
But, what your talking about, head swap into your 5068 and fiddling with the optic is completely possible.

I understand. Let's just call it an experiment.

Its really not that difficult, just make sure you clean the pumps off as good as you can on the outside, and have a clean work area as you will be laying some small components of the pump on it, like the plungers, shoes and rollers.