It'll really bugger up your transfer case and gearbox levers.
Getting the TC lever to work was annoying enough with 2" (it either hit the back of the consol and wouldn't go into 2WD, or hit the front and wouldnt go into 4LLC). Probably need to cut quite a chunk out of the body to get it all going.
Probably have to get rid of or make a custom piece of rubber to go around them (or put up with the noise and water coming in).
Can't remember how much play is left in brakes and waaaaay too cold to go check now.
Also nothing major, but the earth cable from the engine will need extending. Mine JUST fits with 2" (at the back of engine bay on the passenger side, IIRC).
I think there'd be enough in the steering slip joint, but might want to check.
Any reason for the 3" over the normal 2"? If the lift is to stop wiping out the sills on rock n logs n junk, 2" is enough to get the sills above the chassis rails, so should mostly fix that. If not, get sliders. I guess the other reason to do it is tyres. I got no comments about that as I don't want to go bigger than 32's (maybe 33's one day), which fit fine with 2" lift.
Anywho, ur call. Good luck and have fun.
*edit* CR^P... Just read that ur's is 1989. All of what I said is re: 1993 NH. No idea what-so-ever what's relevant.