Are you 2wd or 4wd? If the spring length is the same or no more than a tad longer, and you are 2wd, I think the 4wd rear p/u springs are taller, and if just longer, get a spring shop to re-arch them to the right length, which gets you a little lift right there. Re-arching higher to a shorter length would require a somewhat longer shackle that would lean more forward at the bottom - a little more initial stiffness.

I kind of don't like just a longer shackle. This changes the pinion angle and unmatches the front and rear ujoint angles some. You also get more level ground clearance to the body and frame, but the longer shackle with the same basic spring height does not improve the departure angle, since the angle from the tire to the shackle is the same. You want to increase basic spring height, and with fixed front shackle, and minimal rear shackle longtitudinal tolerance, you have to have a spring with a higher (if you hold your head upside down) arc.

A good leaf spring shop can take your leaf stack apart, untemper the leaves in an annealling oven, bend 'em on a tighter curve, and re-assemble the stack with neat teflon slicky strips between leaves so they are as smooth as coils.

OR, coilover's in place of the shocks, with adjustable spring seats to change the ride height, and maybe take a leaf or two out of the leaf stack.

OR (TAH-DAH), the rednek solution. Air shocks and a big Gabriel sticker for the bumper.