[Altec]

To do custom length shocks the best way to get the length you need is to jack the truck up by the frame, and measure from the shock mounting point on the frame, to the shock mounting point on the axle. Add roughly a inch to that just in case. Then measure the distance from your bump stop to where it touches the axle (Don't forget to compensate for the rubber compressing).

Take the length you got from your first measurement from frame-to-axle, and subtract the distance you got from you bump stop-to-axle measurement and you have your compressed length.

Most will tell you to flex the vehicle out as much as possible to get these measurements. Granted, this will tell you if there is any forced droop on the leaf springs from the axle articulating, but for the normal person it isn't necessary. At that point I'd probably be looking at limiting straps anyway...