A stab in the dark, but I had a similar problem on a Ford 6.9 diesel. It turned out to be a weak starter, not turning the engine over fast enough when it was hot.
2004 C240 Wagon 203.261 Baby Benz
2008 ML320 CDI Highway Cruiser
2006 Toyota Prius, Saving the Planet @ 48 mpg
2000 F-150, Destroying the Planet @ 20 mpg
And remember folks, Only You Can Prevent Hilliary.