We just bought a 2006 Pathfinder SE and the rear suspension feels like it bottoms out when you hit large bumps at highway speeds 70-80 MPH. Has anyone else experienced symptoms like this and if so is there any way to fix it. Any help is appreciated.

 

My problem is the opposite.. at very low speeds, there is a vibration and bbbbbbbbbbbbbbb sound from the rear. Almost as if I am holding the breaks moving forward slowly. I've also noticed my oil pressure gauge jumping around, i.e. going up when i acelerate, and going low when i decelerate.
Anyone see that ever? Does that just mean I have oil pressure problems? Also, I use regular fuel in my pathfinder, if that makes a difference.