Dodge dropped their big block, Ford's big block is a SOHC V-10 that makes 362HP. Even though the Ford gas V-10 is only a $700 option versus the $8000 Powerstroke option which only pushes 350HP, the Powerstroke outsells the V-10 several times over. For Ford Super-Duties, first choice is the Powerstroke, second is the 300HP V8, and last is the V10, even though it's not much more money.
Ford will probably retire their Big Block as well, at least from the pickup line. Not sure when, because at least the Ford is a fairly modern design, and it's based on their V8, which it shares geometry and parts with. It's a 5.4 with two added cylinders, so it's not a big expense to keep it in production.
Diesels killed the big blocks when the HP hit 300. Better fuel range, better tow platform, lower fuel bills.