I have one in my XTerra and agree with the guy who said it's a fuel hog. I think the best I've ever gotten even with the 6-speed was about 17 mpg, pretty much all highway. Usually it's around 15-16, of course that's with the off road package so it's 4wd with large aggressive tires and sits a bit higher than the regular 2wd as well. I've seen as low as 12 loaded down with gear, pulling a trailer full of more gear, with a pair of kayaks on top driving into the wind. Same load without the headwind got me 15 mpg on the way back. At 173k miles, the whole truck doesn't leak a drop of anything, and the oil level goes down maybe 1/4" on the stick between 5k OCIs with 5w-40 HDEO. Earlier ones (mine included) had an issue where the timing chains ate through their guides and made it sound like there was a supercharger under the hood, fix is of course expensive but I took my time and DIY'ed it over the course of about two weeks while also replacing the water pump, belt, idler pulley, and just giving the thing a good once-over.
Changing the spark plugs requires pulling the intake. Go with iridiums and it's probably something you'll only have to do once.