The Nissan Path

Hi, first post, sorry if this has been covered elsewhere. My 94 manual pathy has a strange habit of a big wiggle when I shift gears or if I quickly back off the throttle. Seems even more pronounced when trailering. It is a sideways wiggle that you can even see when it happens as the rear of the truck goes left and the front goes right Feels like it may be from the rear but honestly not sure where it originates from. I've been under the truck repeatedly looking for a culprit but have not identified one yet. I have checked all suspension joints, chassis to frame joints, etc but no dice. Many new front suspension parts have been installed but no change so far. I'm out of ideas and need some help! Thanks in advance.
Bill