check the batteries. when we load test the batteries on diesels in our shop we almost never use the carbon testers (toasters) with diesels. if the weather is not really cold, unhook one battery and crank the engine over, if it cranks fine, swap to the other battery. occasionally you will have a weak cell in one battery or just one battery that has less reserve, after sitting for a while the battery will not have enough juice to continue cranking through the compression. after driving around the battery will have a complete charge until allowed to sit for several hours which could
account for not having any more episodes.
on the other hand, maybe your truck is lactose intollerant?
steve