My f250 6.0 was running fine. Shut off truck, 45 mins later, crank, no start.

Oh my goodness, where to start with this vehicle and engine... It all depends on what else has been repaired in the last 14 years. There are so many places to turn to on this engine. You have to start with basic testing and go from there. There are quite a few guesses, like the STC pipe to the oil pump that can cause weak oil pressure to the injection system, and so forth. Find yourself a skilled 6.0L Ford Diesel tech out there, that's an invaluable resource for anyone who has one of these vehicles.