Tulsa....Don't hold your breath waiting for further incentives,In fact GM prices are about to increase.There is in effect now a 3k cash back to dealers that you may be able to squeeze part of out of your dealer.
I have been working with 6 dealers since last Nov to get the best possible deal for the DTS I ordered two weeks ago.Prices in various locations are different but you should be able to negotiate a price at least 6.5k off MSRP or about $22-2500 off invoice.
Buying a new car and getting a good price can be tiring as the salesman does it daily and you may not even do it yearly.Do your homework(Edmunds,Kelly,NADA etc etc) and try to be patient.Good luck....
