We have a 2014 Landmark that weighs 14,100 lbs empty. For the last year we have been towing it with a 2011 GMC 2500 Duramax. While it is a great truck and perfect for a smaller/lighter 5th wheel we decided for a number of reasons to "upgrade" to a GMC 3500 DRW. The 2500 is now for sale and it is in perfect shape and has less than 34,000 miles on it.
If your looking for a great tow vehicle, check out the following link.