Thanks, Chris_Rob. I've come across several mentions of owners of this truck wanting to upgrade to the 56 because of lack of power. Your assessment is looking like another nail in the old 55's coffin...

What do you know about differences between the injector pumps in the two engines? I heard that the 56 uses a computer-controlled pump?

Incidentally, it is true that the 56 was never sold here in the States, but that doesn't mean they can't be had...