We've pulled out Silverback 29RE with both a 2011 F-250 6.2L gasser and our current 2013 F-350 6.7L dually. We traded the because of the weight restrictions of the F-250. We were right on the edge of what we could tow with only a couple hundred pounds safety margin. That said, the diesel makes the driving a lot more pleasant. The gasser always seemed it was working near it's limit while the diesel hardly notices the trailer at all.
The initial cost is something like $8,000 more then a gasser, the maintenance cost is also higher (it takes 13 quarts of oil, after all) and the new EPA required stuff makes then a lot more complicated.
That said, I'm not going back to gas anytime soon!!