it is not uncommon for the plastic chassis to be tweaked from either building or just driving and hitting a bump wrong.Although most of the time this does not make a drastic change it will make subtle changes especially noticeable if you run the stabilizer plate.I would suggest getting a tweak station, measuring left shocks compared to right shocks at full extension to make sure they are equal, measure the left to right rods to the locker arms with calipers as well to ensure they are equal length.once you know the suspension is equal left to right set the chassis on a level surface with no tires, check to see if it rocks corner to corner in any direction.
After determining either way if the chassis is suspect make efforts to straighten if needed by giving it a bit of a twist, put the wheels on and sit the car on a tweak station to see if it levels out.
Level the car with the rods not the shocks.
Once this is done ensure the camber and toe settings are good and equal left to right and then finally re-check the tweak before trying.
Enjoy.