I have a 97 pathfinder 4x4 4wd, and i have the same problem. I got the struts replaced as of now...and it helped with the front bottoming out and some of the suspension wobble. But the rear shimmy at high speeds is due to a suspension problem in the back.
I heard that this shimmy problem is the rear link (control) arms and bushings... there is a forum (
pathfinder problems - Topix) where about 100 people with our exact same car have the exact same problem. You can check that out.