Interesting thought. I'm going to call the dealer and ask. I agree a diesel will not respond like a gasser, I currently have both and can attest to that. But none of my diesels are as bad as the ED with the lagjust to clarify my statement about the nature of a diesel, it was in comparison of a gas engine and the initial "lag" of an instantaneous gas throttle.
Sounds like you may have a problem, wonder if the dealer resets your ECU/TCM so it goes through its learning process again would help?
I have also drove the Cummins, Powerstroke and Duramax, I personally noticed an initial lag in all of them, but nothing to the extent of what sounds like is happening with yours.