On diesel engines that will not restart, after they are warmed up, it's often a sign of a tired fuel pump. As they heat soak, inside pump head clearances increase and it will no longer develop sufficient fuel pressure at cranking speed. While it's running, fuel helps cool the pump by carrying the heat away. Replace the fuel pump, change both fuel filters, and the problem will likely go away.

I replaced the fuel pump 8 months ago. I have noticed an oil leak under the truck recently. Haven't pin pointed it yet. Does the 6.0 have a high pressure oil pump for the injectors, like the 7.3.

Yes, read Item 6 below:

https://www.askmehelpdesk.com/cars-t...ml#post1415281