If you`re talking about the newer diesels (in the last couple of years), skip them and go gas. there is no way I wasn't the issues the new diesels have! yes they have more and bigger problems than the diesels from before 2010!
Right now I would go gas. my 02 V-10 has no problem towing 9200lbs. even though it gets mid 7`s towing, I know I`m going to get to my destination without issues.