Nissan makes a 5.6L V8.
I don't really know any thing about the Armada, but I can tell ya the 3500 NV passenger van does just fine with that engine powering it dragging our 35 foot TT around ( BTW, a Passport 31RE , somewhere around 7500lbs loaded). We did nearly 4K miles on one trip / 12 days last summer. I find it very comfortable towing. 10K miles of towing over the last 2 1/2 years. All good experience once I ditched cheap brake controller the RV dealer initially installed.
We don't have a huge gang of 8 kids or anything like that, but bought the van to have all that interior space / rows of seats for travelling comfortably for 4 to 6 adults with plenty of space for gear / luggage and it was about $10K less than anything else with even just close to the same seating and towing capacity.