For a 93 Trooper, all you HAVE to have for 3" lift is OME 912 springs and 2" coil spacers, along with torsion bar crank. 919 springs might give you another half inch. If you want to make your own spacers, look at this: http://myweb.cableone.net/bcanderson/trooper/coils/coils.html
I don't know how well these have held up, but you can email Bruce Anderson and see how they are doing.

Other stuff you probably should get:
-Longer shocks to take advantage of the higher ride height. It will allow a little more downtravel, especially on the rear axle, but this is not required. In the front you can put a spacer at the top of the shock and acheive the same thing.
-Ball joint spacers and low profile bumpstops for a ball joint flip, gains back about a half inch of downtravel up front which is a good thing.

You might note that the above is pretty much what you get with the 3" lift kit from Independent4x.

If you are going to wheel, other stuff to consider, in no particular order:
-rocker panel protection (highly recommended)
-diff drop brackets to relieve angles on CV joints (DOR)
-tie rod shields (DOR) or keep spare tie rods with you
-extended/tougher brake lines (Indy4x)
-remove rear sway bar, which limits rear axle articulation, and does not affect ride much
-tougher rear axle links (Stinkyfab)
-manual hubs (the auto ones will unlock everytime you back up)
-Teralow transfer case gears