1999 Lexus RX 300 This car dips in nthe rear when you acell

This car dips in inthe rear when you accellerate and wanders left and right as if the lug nuts were loose They are not. We tightened up the steering and checked the rack and replaced the tires and replaced the rotors which were bad (unrelated). This does this upon accelleration and while just going down the road as I said. Is it the Struts? How much are they to replace?