In my opinion no matter what kind of numbers the Izuzu engine is coming out with there is no way in size shape, form, that V8 will every accomplish in low end torque or mileage numbers compared to the Cummins...
It seems to me that most of the reason they are making more hp and tq numbers is because they got a hot seller at least they are moving some trucks, and most that are buying it are young guys looking for the hot rod diesel, don't get me wrong their are alot of dodges running around that only see burnouts and parties...
if your saying 650hp/360tq. . or did you mean the other way around, i wouldn't trade my 92 12V for those numbers, i don't need Hp, guess most have forgotten the speed limit hampers the use of those extra horses, with the cummins your getting much more... I don't think i would worry to much or get upset, just remember you have a far more superior, bullet proof engine than any other truck on the street when it comes to diesel engines. Plus with the upping of Hp and torque so does the price tag, for what a diesel engine with aluminum heads and made by Izuzu