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. If you install them, they are now yours, there are no refunds on shocks that you bought that are the wrong length and have been installed. PERIOD.
We offer an assortment of Bilsteins to match your ride height, from 0-12" of rear lift. They are superior to the factory shocks in nearly every way and come with a limited 90 day warranty. Since Bilstein doesn't make a direct fit 5125 series shock for the Titan, we modify the ends so they are a direct fit for your truck.
Please note that the price shown is for a PAIR of shocks. We make the crush sleeves the same dimension as a stock shock, often aftermarket shocks will have narrower crush sleeves and this make these difficult to install with first bending the stock mounting tab a little back into shape....not a big deal but worth noting. 
The length of the rear shocks is determined by the amout of lift on the REAR of the truck...you can have 10" of front lift, but if you only have a 2" rear block, then the rear has 2" lift. The following is a brief list to help determine which shock is best for your application. Another way to tell is to measure from upper to lower shock bolt at ride height....add about 4" to determine the overall lenght of the shock needed.
-1-2" drop 2wd/2-3" drop 4wd 22" long
-0-2" 2wd/0-1" 4wd 25" long
-2-4" 2wd/1-3" 4wd 27" long
-3-5" 2wd/2-4" 4wd 28" long
-4-6 2wd/3-5" 4wd 29" long
-Taller than this go with a 31" long shock
More notes, Titan shocks will not bolt onto an Xterra or Frontier...the mounts are different.
Even more notes, we generally ship these shocks with the boots mounted UP (body down) as the bodies are easy to clean and can be seen from under the truck. If you want a racy look, we can mount them body UP, the boots tend to turn brown over time...but you can cut the boot off and it looks good too. There is ZERO performance difference either way.