If your batteries, grounds, glow plug relay, all 8 glow plugs and uvc harnesses are ok. First I’d look for obvious things like making sure it has enough oil in it& checking for fuel or oil in the valley. Make sure neither of those systems are leaking down causing a loss of prime on either system. Second I’d make sure the oil reservoir is full and not leaking back. 3rd I’d check to verify my cranking rpms is in excess of 250rpm, base engine oil pressure is instant and minimum icp reading is 500 while cranking. If it is stumbling and/or has white/grey smoke the excessive fuel could be from continuous cranking and not necessarily a bad/worn or leaking injector.
Does it restart hot? (170+* coolant temp after letting it sit for a couple minutes) If so, is white/grey smoke present upon hot restart? Is it stumbling? Do a buzz test and a cylinder contribution test. If the valve covers are off, make sure all injectors are properly tq’d (you wouldn’t believe how many hold downs I’ve seen loose and had to re-oring the injectors)
Do you run oil and fuel additives? What mods are done to the truck? And is there a specific temperature it starts to act up at? (35ish*?) I’m assuming it cranks for 8-12seconds before it starts?? Do you have a block heater? If so and you plug it in does it make a difference?