Our newest work truck is a 2015 Chevy 3500. It's a double cab, 4wd, with 4:10 gears. It has a service body and ladder rack and weighs about 9,000 pounds "empty". The heaviest I've towed was about 13,000 pounds. Going up a mountain with the pedal on the floor I was doing about 35 MPH. It got me to the top with no problems but coming from my personal Duramax truck I couldn't stand towing like that.
If you've suffered thru the 2005 Ford 6.0 debacle don't let that be how you judge diesels. We've had two Ford 6.0s at work: an '03 and an '06. They've been nothing but trouble, expensive trouble. My experience with my personal trucks: an '05 Chevy Duramax and an '07 Duramax has been wonderful. The '05 has 205,000 miles on it with hardly any problems at all. It's been the most trouble free reliable vehicle I've ever owned.