Shocks and springs are a good idea , I've had new shocks with the same sagging ride height because the springs were worn out.
You can test the shocks with counting the number of bounces it takes to stop. Odds are if there original they are shot.
I don't know if there is a set that fits the KJ but monroe sensa-trac load adjusting shock absorbers can help lift a sagging suspension. They are a shock absorber with a spring around it, kind of like a strut assembly.
Work great on a old Cherokee with sagging rear leaf springs and they make them for newer grand Cherokees as well.
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