NOTE: Rear shocks do NOT offer lift by themselves. Rear shocks need to be matched to the amount of REAR lift you have. I cant believe I need to include this info but apparently I do.
We offer the 5125 series of Bilstein shocks for just about any amount of lift on your 2005+ Xterra. Listed are the popular sizes, please call if you need a custom length. The price is for a pair of shocks shipped in the 48 states. These are super-easy to install and can be done with the tires on the ground and at ride height with simple tools. Note; be sure to tighten the upper nut until it stops against the shoulder of the mounting stud. An issue has been not tightening the upper nut and eventually the shock will come off the upper mount and grind itself to oblivion....this is NOT covered under and warranty.
Some commonly asked questions;
-How do these compare to the Radflo Emuslion shocks on my Xterra? These are great but with the Radflo rears you do get a much more composed ride. If you run with a rear-mounted spare these bilstiens are awesome, if you run 100% stock these will be a tad stiffer than stock but with much better bottoming resistance than the stock shocks , and these ride much better than the stock Bilsteins. 
-What is different between your 5125 series Bilsteins and 5125 sold by other stores? We modify the ends so that these are a direct bolt on...that is where the little bit of extra cost comes from. Some vendors are sellign these but to save cost they keep the stock bushings, this makes the crush sleeve so thin that it can buckle when tightened. We also install the bushings to save you the hassle.
-Do these mount body up or down? The Bilstien mono-tube shocks can mount at any angle but we build them body down as the black boots turn brown-ish over time and dont look as good as a shiny silver body. You can easily mount them the other way though by just pressing out the bushings/sleeves we install and flipping them.
-Do I need to run boots on my shocks? Well, these come with boots from Bilstien and we ship them that way. The boots seem a moot point...keeping some dirt out, but keeping some dirt in. If you want a race-y look, cut the boots off and mount them body up. Again, 100% preference, no performance gain or loss no matter the mounting direction.
-Is there a waranty? Yes, it's 90 day LIMITED. meaning, that they will need to go back to Bilstein for inspection. But call us first as we may have other solutions. We offer these in many lengths. Pice from the list below. An Easy way to tell how long a shock is required is to measure the existing shock at ride height (tires on the ground as it normally sits) and add 2-3" to get the extended length. If you are lifting it, be sure to add the amout to the original number. Example; as it sits you crawl under there and form bolt-to-bolt the shock measures 16.5". You are gonna add a 2" lift AAL, your total will be 18.5". Add 3 to that for 21.5" and that will be the length needed. If you order a shock that is too long, it will bottom out sooner. 
Options:
-20.5
-21.5
-22.5
-24