PRG/Deaver 10 leaf race spring. This is the smoothest riding rear spring available for your Frontier and offer 3" of lift. This kit includes the springs, u-bolts, and urethane bushings (which we custom machine to eliminate squeaks and offer most articulation and smoothest ride). Longer shackles are NOT required unless you are running shocks through the bed. At that point these springs will offer a up to 16" travel when used with a custom shock hoop and appropriate shocks. But the bolt-on shocks we sell work incredibly well when combined with these springs. Please order and we will contact you for the add'l shipping. Please note, we used to advertise these springs with a slight loss in load capacity, these newest version will actually carry a small load (couple dirt bikes or camping gear, or camper shell, etc) much better than the stock springs and will offer much less spring wrap when towing. These are not designed to increase load capacity though, but you will not loose capacity. Average install is about 1-2 hrs and can be done with basic hand tools. These are built on a limited basis...we usually have them in stock, but if not, there can be 8-12 week lead time.