It is not a question of gas versus diesel when the Ford trucks with a gas engine are not rated to tow the planned weight. Two choices, go with diesel or get a lighter trailer.
It is amazingly simple minded for someone to state that because they have not had to spend thousands on diesel engine repairs that this is the norm. I don't know specifics about the Cummins used in the Ram pickups but the GM and Ford diesels have all had their share of problems that cost $4,000 to $15,000 repair and lots of these repairs were needed on engines with less than 100,000 miles of use. Easy enough to scan the diesel forums and find the information.
When I read all the problems with the diesel engines I decided to buy a new truck and get the warranty instead of buying a used one. With gas I would have been comfortable buying a used truck.