I have the 6.5, with the newr generation block (cause the origional blew at 180,000) its not a duramax by any means and my old 454 would kick its you know what in a flat out drag race, but this one keeps up pretty good and is good on fuel.
I personaly would do a 454, and actually I have an '82 with 120 something thousand KM (about 60,000 miles) on it that I am lookin to get rid of.
I went from a 350 (suburban) to a 454 (crew dually) and went almost 800 lbs heavier at the same time and actually got better fuel mileage while towing with it.
