HELP! Needing some information for my s13 hatch

[Nwfilms]

Im in the process of a build with my s13 and had a couple questions as to why my car is functioning like it is.

when im on the freeway or doing anything over the speed of 40 mph my car likes to sway back in fourth in the rear more than my other 40's..? the car all around just doesnt feel right and im wondering what could be the main cause to this.

im almost 100% positive my subframe is straight and i have

rear upper traction arms, rear camber plates, and some other goodies in the rear but i still have my OEM sway bar in the rear as well, could this be a problem?

possible subframe bushings??

im very unsure and would like to be pointed in the right direction. all my paychecks go into my cars to if i know what i need to do that would be a huge help!

Thank you for waisting your time on my thread