There is something limiting the ICP. It does the same thing when you have a bad CPS, the PCM will hold ICP low to prevent the injectors from firing. If the PCM was trying to fire the injectors, ICP pressures would continue to rise as you crank the truck.

So something is wrong, the PCM sees it, and it's not letting the injectors fire.

How long do you crank? Have you tried extended cranking for 10-15 seconds? If not, here's something to do. Clear all codes, crank the engine for 10-15 seconds (make sure the starter is cool before you do), then recheck for codes. See if anything new pops up.