Thank You, All, for your replies. My BIL, sister and I really appreciate your thought's, suggestions, experiences, etc.
Regarding the car hauler (enclosed), I believe I remember my BIL saying that the weight rating is around 7,000 lbs. I believe it has 15" wheels, on it. So, at this point, it will not be a heavy load for just about any diesel pick-up, 2500 or 3500. They have not towed, before so, are not really experienced in towing. For years, I have towed a 25' travel trailer that weighs pretty much the same as this trailer will weigh, loaded. So, I have an idea of what they are up against. I just want them to have a good experience with the truck they choose and have more than what they need in a towing vehicle. Either the Duramax or Ram will accomplish their task. They have bought 6 acres in North Scottsdale and the neighborhood is "horse property" so, there is a chance that they may be buying a small tractor, side by side, and collector cars, which, will be somewhat of a hobby, for him. I suggested the diesel as it will most likely do anything that he will encounter, in the future. They, also, are looking forward to traveling around AZ. in the mountains & deserts along with hitting the National Parks that we have in abundance here in the Western U.S. They like the idea of a vehicle that sits high thinking that if they ever get hit in the side, they will be safer. Again, you folks have come up with great suggestions and recommendations and I appreciate the info. and comparisons with older Dodge/Rams to the newer models. Thank You, again. You all are a wonderful resource that I have used in the past, many times, over the years. You didn't disappoint. If you have more suggestions, please continue to respond as I will continue to monitor this thread and am sending it to my BIL & sister.
Buffalo Joe