You might consider replacing the rear control(and lateral) arm bushings while in there. I found it made a fair improvement in getting rid of the "sag" on our 1990 4runner. I used urethane instead of factory bushings. After so many years and miles, those old bushings just give so much, which drops the rear down through geometric loss(ie collapsed).
The rear springs I used were Moog 225 with factory shocks.
regards