The shocks you purchased don't appear to be the right ones. I currently have a new 2012 Xterra. Prior to purchasing it in March, I had a 2003 Xterra. When I sold it, it had 150,000 miles on it.

Therefore, I went through several sets of shocks. The first set, naturally, were the factory ones which came on the truck when I purchased it new. I believe they lasted around 60,000 miles. I replaced them with Bilsteins. The bilsteins are definitely a well-built shock and they never leaked, broke, or obviously failed in any way which would have entitled me to a replacement under the warranty.

However, after approximately 30k or 40k miles, I perceived that the quality of the ride had deteriorated. I guess I felt that the Bilsteins had not been worth the money I had spent on them. I therefore replaced them with one of the commonly available, reasonably priced ones. They might have been Monroe shocks.

Having had all that experience and perspective, my advice is this. When replacing your shocks, replace them with the Nissan ones from the Nissan parts department. I don't know who makes them. But they are damn good shocks. They make the truck ride well when new, and I must assume they will do the same at whatever mileage you replace them at.

Keep in mind that other things can affect ride quality. Perhished control arm bushings, bad ball joints (usually the bottom ones), worn out or improperly adjusted wheel bearings can all be to blame. And don't forget that torsion bars don't last forever.

But when it comes to shocks, for the money, you can't beat the OEM ones. And if you purchase shocks, or any other part, from the Nissan parts department, you know you will get the right part for your vehicle. Regarding cost, one reason that I have purchased new Nissan vehicles since 2003 is that the parts are very reasonably priced. In addition, since I do all of my own maintenance, I purchase quite a lot of parts. I therefore requested and received discount priveleges at the parts department. All you have to do is ask the parts manager. And then, every time you go to the parts counter to get and pay for your parts, remind them to give you your discount. It's as simple as that. I get 20%, but I imagine that I could get more if I asked for it. And, in the case of very expensive parts, I often do get better than 20%.