According to the factory service manual you should also loosen the bars that connect the front suspension to the frame at the front of the truck. Don't take them off, just back off the bolts a bit. Then once you have the level you are looking for they should be retorqued to spec. (Which I don't remember, but its in the Haynes service manuals)
I should also stress you should support the frame of the truck while you are adjusting the torsion bars, I broke the adjuster bolt on my 4x4 when I was working on it. A block of wood I had under the frame "just in case" caught the truck on its way to the floor.
Sounds most likely that you are already dropped in the front and it has hit the bump stops. You can get low profile bump stops made from poly to replace the stock one. 4x4 shops would be a good place to look for them, like
www.independent4x.com
_________________
95 Isuzu Trooper Daily Driver
86 Isuzu Trooper reliable backup
77 LUV 2wd stock beltway blaster (resting)
79 4x4 LUV project: 2.6L, 5spd, 31s (eventually)
MEPR: Man, my 4x4 makes all other LUVs look good