This death wobble is notorious in '03 Pathfinders. Once you hit 55+ mph, the car would violently go into a wobble and you must let off the gas and it would stop. Replacing the rear control arm bushings immediately fixed it. They are put on with 240 foot lbs of torque so use a 17mm ratchet to remove, not a 3/4 inch like I did, because you will strip it and it will become an all weekend project to remove the bolts. While you're at it, I would replace as many of the bushings as you can for a smooth ride. Even with the suspension problems, I still love this car.