The 99 rears had sag almost as soon as I loaded any weight in the back. Like I said I carry roughly 100lbs of tools/recovery gear on average, and that was enough to sag the back just under level for me. Towing, or transporting heavier things like tool boxes, my little 4x6 band saw, lathe etc, carrying that stuff was the biggest reason I wasn't worried about having some rake unloaded.
As far as the shocks, same part number for any factory replacement style shock from 96-02 (at least as far as I have ever seen).
As far as the ride .. 100% unloaded was a little stiff, but nothing you couldn't deal with. Since changing to the new tires (e rated 10ply) the ride is on the firm side for sure... still not unbearable, but getting close.