There should be a yellow sticker inside the door on the Nissan that says something like "Combined weight of cargo and passengers should not exceed ______ lbs". What does that yellow sticker say. With that information, we would be better able to answer your questions.
The short answer is: you can pull a much bigger TT than 5th wheel with any given truck due to pin weight (22%±) vs tongue weight (12%±) being a lot more for a 5er vs TT.