The Duff springs are about 400ppi compared to 500ppi for the stock ones. They are for highspeed use more than anything. The whole kit was originally designed for that kind of use I think. With the double shocks and those coils I could have road-raced my truck. The long arms help the vehcile stay in alignment on high-G turns on the road course. For an average offroad truck they are too stiff and the shock mounts aren't far enough apart for what's available. I would not buy the new Duff kit because I don't see how you can work within the confines of that shock setup. On the old kit I moved the hoops to use longer shocks. You spend your money for the rest of the parts but the coils don't let you use the improved geometry. I won't say Skyjacker is better because each vehicle needs a different coil. But to me Duff looks like they developed the original kit from their stadium truck and Skyjacker is a more offroad type of kit. I do love my old DUff radius arms and they do make good drop brackets. The new kit, I don't think so. I liked the old hoops.
One thing about the DUff springs. They are supposedly variable rate springs. This is not exactly true. Some of the coils are closer together, but they do not touch at rest. The only time they touch is when you crash down hard on them. For most of us, they are single rate coils. For a stadium truck, that's great--it won't bottom out.
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