I owned a 2004 Armada and now have an Infiniti QX56 (same vehicle, shiny rims). My brother also owned a Nissan Titan. I've towed with all three and they do pretty dang good. I was impressed with the power and the transmission (5-speed auto). I would definitely want trailer brakes and a good brake controller if you're hauling a rig around. I'm not a huge fan of the IRS (independent rear suspension) but haven't had any issues yet. They are built decently, the only issue we've had on either was the brakes warping, but they had a major recall campaign and most/all of them were fixed.
I've also towed a bunch with an Chevrolet Avalanche that has the 5.3 and 4-speed auto (new '09's have a six-speed auto) and I would say the Nissan towed about the same or better (I think the Nissan's were a bit better as far as not wanting to hunt gears and the Nissan's just seem to have more power).
Good luck, drive a few Nissan's if you go that direction... our Infiniti seems like a completely different vehicle than the Armada (less rattles, noise, etc.) and they are both 2004's with the same miles (Armada was new and the Infiniti was used).