Well, Consumer Reports says they're getting better..
Consumer Reports Dings Ford and Chrysler, While GM and Audi ImproveI have an 01 half-ton Suburban with 190k miles that has had a hard life, and it has the original engine and transmission. Wouldn't think twice about loading it up for a 1,000 mile road trip.
The '08 2500 has been awesome - greater towing and payload, yet nicer creature comforts and options. Both tougher and more refined at the same time.
Half-ton GMT900 trucks are burdened with the AFM - search Google for AFM 5.3 for some light reading.
The heavier-duty trucks are good to go. The 6.0 motor is absolutely bulletproof, and paired to the six-speed makes for a great tow vehicle. No personal experience with the DuraMax diesels, but I've seen/heard good things. Nothing like the Ford 6.0 powerstroke.