Great truck for the ride & comfort. The 6.6 Diesel has exhaust re-gen problems, GM says there is no fix, get used to the smell of exhaust in the cab. I would not recommend the $8,000 for the diesel, go with the 6.0 gas engine. I get 7-8 MPG pulling a 34' 5th wheel...lots of power, lots of exhaust fumes to contend with. The Allison trans is a great feature!
Chevy has done a great job of combining comfort and usable power into one vehicle. I use my 3500 to tow a 35 foot fiver through mountain areas with no problems. the Allison tranny is great for hauls done or up long grades.