For 96, which has no pesky axle disconnect, I'd start with the linkage, especially if it's also stiff.
First, of course, you need to get underneath and confirm that the linkage is all there, not bent or broken. The basic drill for adjusting a 231 linkage is pretty simple. You'll see that a part of the linkage is a round rod that goes through a trunnion with a bolt in it. You loosen that bolt (doing whatever you need in the way of lubing and derusting to get the rod to slide freely in the trunnion), then use the lever on the TC itself to shift it all the way into 4 low. Then go up and shift the lever into 4 low. Then go back down and tighten the bolt. When you're done, the handle should be more or less parallel to the floor when it's in 2 hi.
If you don't exercise it frequently, the lever will tend to get stiff, especially where the shaft passes through the floor. It's a good idea, every once in a while, just to sit there and shift back and forth with the engine off. Do it about 40 times in a row, and it will usually free up.
