Spoken from experience. Towing a sailing boat up and down the east coast for racing. Its not that the smaller capacity engines are not capable of towing loads, they can and I have done it. However when you stick 2 tonne of boat with high windage and you want to do the speed limit, they spend a lot of time jumping down gears and revving high on the very smallest of inclines.The V6 3.0 still does it, but needs a much larger incline before it becomes a problem.
Have to admit, My navara is leaf sprung at the back, and so was the previous one. All the vehicles I have towed the boat(s) with have been rear leaf. Maybe the coil spring rear is better? From memory Nissan did do an upgrade to the rear springs of the NP300 because it was a known problem when loaded, so perhaps they have finally sorted out the shit suspension. Time will tell. However, myself and pretty much every one I know that tows a decent load with the modern crop of 4wd utes has needed to replace the suspension at around the 50000km mark. I am not bagging the utes because of this, just saying its yet another one of those compromises that you need to be aware of.
If you jump in a modern landcruiser ute and compare it to navara there is a clear difference. The LC is a great car, plenty of grunt and can tow a house. But the Navara is like jumping into a Commodore sedan, much more comfortable and better car for touring and city driving. Everything is a compromise.
Me personally, I just wish the manufacturers would step it up just a little, something halfway between our current crop of dual cab utes and the yankee ones. The 3.2l ranger is close, maybe just push it out to a 4.0! Just bought the wife a new car today, talking to the salesman and there is a rumour that Nissan might be bringing back a larger engine in the Navara. If I was to take a wild stab in the dark and if there was any substance in the rumour then perhaps it might be a Mercedes v6 diesel engine?.