96 cutlass has shocks in the rear. shocks retard the bounce from the springs as they recoil. shocks are filled with gas usually, and in extreme cold, they can become ....sluggish.....so you'd perceive a bumpier ride.
if you begin to hear banging noises, have it checked out asap.
it may need new shocks.....($111/pair at
shockwarehouse)
how many miles on it?