[mikestony]

My best educated guess is the 15" wheel option has drum in the rear, the 16" option has disc. You state your car came with 17" wheels? or did someone put 17" on it?
Do you have drum or disc in the rear?

Edit:

 

[mikestony]

Came with the factory 225/50/17s when I bought it

Well, how about this.
Can you post your RPO codes? You'll probably find them in your glove box, affixed to the door. If not there, maybe affixed to the underside of the spare tire cover/lid.