So after much trial and error I've finally gotten to a new set of problems with starting the old 7.3. New battery's, new alt, new gp, new gp controller and relay, new oil pan heater and cord. Plug the truck in at night and at work during the day (temps are around 0°F). Cycle glow plugs 3-4 times and try to crank and it's the slowest turn over possible, it starts speeding up but doesn't fire, turn the key off, turn key to on again and she fires right up everytime. Doesn't matter if she's ice cold or been running half the day and only shut off for 20 min. What could possibly be the problem here?