If you want to level it out, you might consider MOOG coil springs(#225) and replace the rear control arm bushings with urethane(suspension.com). Get them sent to Blaine and pick them up.
The rear suspension sag on these is not just spring failing, it's the bushings as well. The springs are about $80, and the bushings will probably run about $40. You'll be stunned the difference those bushings will have on the truck(better handling, no sag, etc...).
regards