Nowhere was that more obvious than in the company's August sales, which while undisclosed, predictably leaked with Bloomberg reporting that in the last month, GM sales plunged 13% for the same reason most other automakers saw a sharp drop in July sales: a sharp pull back on sales incentives, especially for full-size pickups.

In addition to the biggest drop in years, GM's total sales also missed analysts' average estimate for a decline of 7.7%. Speaking to Bloomberg, company spokesman Jim Cain refused to comment on the sales drop, but he did confirm that GM dialed back discounts during the month.

The report extended the decline for GM shares, which dropped 1.3% to $35.58. The stock is now down 13% YTD.