Very easy assembly. I raised the rear end under my hitch with jack stands. You don't need to remove the wheels to install this product. Also, you don't have to remove the spare tire under the pickup truck. When installing GMT800 models (99-06 Sierra, Silverado or SUV models) on a truck, the bolt and nut size is 21mm. It is recommended to use wd40 on screws before removing. I used a 21mm wrench and 21mm socket on a hand ratchet. It is very easy to remove the old shock absorbers and install new ones. You don't have to compress the new shock if you jack up the rear end by the hitch rather than the axle. Be sure to mark the wheels with chalk and use proper jacks. You want the rear end to be high enough to allow the tire to lift off the ground when jacked higher. For this reason, it is very important to use crayons and bushings together. New shock absorbers are present. I recommend installing the bolt and securing the top end of the shock before installing the bottom. (It makes it easier, trust me). Do not fully tighten one end of the damper before installing both bolts on both ends, this will provide better movement. Once both bolts are through, you can use a wrench to tighten the nuts. This product does not come with new bolts or nuts, so you will need to reuse old ones or find a suitable replacement at a hardware store or auto parts store. dress tight. Use a torque wrench if you want. You'll find that this adds about an inch to the back end. Very good quality product and made in USA. Very happy with the trip.