Take the front shocks out and see how much resistance you have.You should be able to move it fairly easily. If the front suspension is bound up some where, fixing that should get the front to work. The rear springs may need some attention also. What is the shackle angle at the back? Is there enough travel in the back shackles to allow them to work? Are the springs too high of a spring rate? With the shocks loose at the rear, the rear should move easily also.
For a real education on leaf springs, go to an AFCO catalog and read the page on leaf springs. Very enlightening, with much information a lot of folks do not know about what can give you trouble.