Chances are the 4x4 was not used much, or at least not in quite a while. The linkage is probable in need of some lubrication.
While shopping for my latest truck I came across a 2000 with the same problem. I didn't even want to switch it to 4 wheel, I had the owner do it. It felt like I was going to break off the shift lever. Finally after sitting in the driveway for a while I proceeded to move it back and forth about a hundred times or so. It became much easier and the owner thanked me. It could really have used some lube on the linkage arms as well.
You should be able to lube it and exercise it in less than a half hour. It will probable shift like new when your done.