1998 Nissan Pathfinder car sways and rocks sometimes

My 1998 Nissan pathfinder runs great, the steering also is fine. It doesn't pull to the left or right, Sometimes when I go 40 to 45 mph, it starts to sway and rock. I need to either press my brakes or decelerate on my gas pedal to slow it down a bit to 35 mph then it runs smooth and when I start to accelerate, again it sways. I inspect all the rear links, and both front lower control arms, shocks, struts, and sway bars. Nothing bent, the bushings they all seem in good shape. Any chance you can tell me whats causing this problem? Did I over looked on my inspection? Tires are all new and balanced out, I thought that would solve the sway and rocking at first but it didn't. Any suggestions anyone? Thanks