We own a 1 ton Express van with the Duramax. I would encourage you to look at those, too. I have been extremely impressed specifically with the Duramax engine. I think its relative quietness makes it ideal for a van if you're leaning towards diesel and want to do long trips.
My sense is they might be a bit more difficult to find and also a bit more expensive than a similar vintage Ford Powerstroke cargo van ('06+), speaking strictly of stock vans. A quick but by no means exhaustive search bore this out somewhat. You might try to find one already converted to 4x4 as those options are limited on the GMs, especially with Quigley bowing out of the lifted, solid front axle market on them.