This is a really easy and cheap ($15) thing to do to help improve what little gas mileage the pathfinder already gets and help maintain it. Whole process takes under an hour to do. All you need is a 10mm socket and a Phillips screw driver. Pliers could come in handy as well.
First, if you have them, back the truck up onto some ramps to help get under the back end much easier and remember to put the parking brake on. Next, pull out the fuel pump fuse located behind the coin drawer below the steering wheel. pull out the 15A fuse that is located between the 7.5A and 10A fuse in the second column from the left. The backside of the coin drawer also has a layout of the fuses if you get confused.
Once the fuse is out start up the truck and let it run out of gas. Do this a few times to ensure you get most all of the gas out of the lines. Once it won't start anymore go to the backside of your truck and located just above the rear axle is your fuel filter.
Next remove the 10mm bolt that clamps the fuel filter in place. If it's anything like mine it is probably a little rusty and can easily brake so be careful removing it.
Once it's out loosen the hose clamps on either end of the filter and slide them down the hose. Now comes the tricky part. Try and twist off the hoses so you don't crack them. Mine were fused in place pretty well so I just used a pair of pliers to grip the hose and twist them off. You can also just replace the hoses all together and not worry about it at all. Careful when taking these hoses off because there might still be some gas in the line so it can come spewing out for a second. Might be a good idea to have a drain bucket under there just in case. Once it is out go ahead and put in the new filter and tighten everything back up. Be sure to put the filter in the correct direction as before, because otherwise you are going to have to do it all over again when your truck won't start.
Once it's all together put the fuse back in and start up the truck to make sure it works again.