How is your sway bar endlinks set up..strut or Control arm.
I would think it's the LCA so pick a 06-11 Impala on Rockauto.

If you are capable of the switcheroo, which you are....go for the FE3s from the 04 or 05 Grand Prix or check out the KYB AGXs from ZZP or wherever.

Otherwise 06-11 Impalas or any year 97-08 GP