I have a 2004 Nissan Frontier Crew Cab, and it has the same engine as yours. I have the Casita
17SD with all the bells and whistles, plus an entire "canopy covered" truck bed full of everything and anything when I go. Travelled a good deal, covered many high mountain passes (over 6,000 ft +), and always had plenty enough power to handle the whole shebang.
You will notice a pretty good drop off in fuel economy while towing...well, at least I do anyways. I normally get around 19-20 mpg without the trailer, and usually see about 11-12 mpg while towing. I would also qualify that by adding that I usually tow at speeds of between 65 -70, with occasional bursts to 75 mph, so I guess if you don't put your foot in it like I do, you may experience a little better fuel economy. All in all, no complaints on the truck being capable of handling it, but I would recommend a good WDH and perhaps some el cheapo aftermarket rear leaf spring boosters. Other than that, it's great.