The 6.6 GAS L8T engine is supposed to be pretty good from what I've been reading. I think the only drawback (maybe?) is that's direct injected. It comes in the HD trucks, so no AFM/DOD or dynamic fuel management.
I think it has the bore of a 6.2 but longer stroke, and cast iron block instead of aluminum. Couple that with the 10 speed transmission, massive 12" ring gear axle and you've got a good drivetrain.
There's companies now making aftermarket port injection intakes so you can "swap" them into other vehicles.