Never use starting fluid. How fast the engine turns is crucial. Check the tachometer.
Often, removing and cleaning battery cables is a fix. How charged batteries are is a concearn.
Power to the glowplugs? When is last time you changed glowplugs? Only use AC Delco 60g or bosch 80034.
How cold is it where you are? Fuel could be gelling.
Have you owned the truck a while or new purchase?
Has it been running ok and just didn’t start this morning or what the details?