I have 2000 7.3 had a similar problem it was glow plugs I would plug in block heater for an hour then it would fire right up, it could be clogged fuel/water separator also, mine clogged from pieces of plastic off of fuel pick up in bottom of fuel tank sucked into electric fuel pump, it would run...
just replaced upper and lower ball joints stub axles hub bearings seals vacuum lines rotors. A couple months ago doing routine maintenance changing out fuel filter water separator element after screwing cap on, started engine checking for leaks gasket blew out sprayed diesel fuel in my eyes and...
