2008 gmc dually info

That should be a great truck. I owned an '07.5 which is the same truck. I never had any trouble with it except for the leaking trans. cooler lines that were fixed under warranty. That was the only thing ever done to the truck in the nearly 40,000 miles I used it for heavy towing and hauling. I sold it because I didn't need it any more.
I don't know about the price but you can't compare it to a 6.0 Ford for resale. Some dealers won't even take those tings in trade because they're so hard to get rid of.