Not so long ago, I had a 2000 F550 7.3L that would not start at times. It came from an indi with a new PCM, IDM, HPOP, IPR, ICP, glow plug relay and lift pump for an intermittent no-start. I guess since there were no parts left to throw at it (other than batteries) they gave up. It took me the better part of 5 minutes to find the modules were not turning on because the voltage was dropping down to 8v when cranking... 2 batteries later, it was all good! It was summer, and by listening to the cranking speed you wouldn't have suspected batteries, but they were both pooched.