I wouldn't discount the WISC III simply because it was an older test. These tests change very little from one version to the next, most changes you notice will be in questions designed to cater to a particular minority group to boost scores of certain groups.

The fact that he has scores all over the place could just be the result of him not taking the test seriously. You might consider taking him to be tested by someone else. If he was tested by a woman and scores were all over the place then you might find a male tester to try next time. Sometimes boys that act up and don't give it their all for a woman will do so for a man, or sometimes they work better for a woman than a man.