If your car didn't come with one and your state requires it, you'll have to place it very carefully, and drill the holes in the bumper. The original ones have an expanding threaded aluminum rivet for the holes. My dealer simply put the screws in the plastic.
As for buying from GMPD, remember they charge shipping and handling, which can be significant. They don't stock parts but rather order them from GM to be sent to your house, so there will be a delay of several weeks. If saving $5 is more important, then that's the answer, but if you want it this month, I'd go to the dealers parts departement. My parts guy gives me a 20% discount, which ends up being much closer to the shipped GMPD prices.
