Hard to say without getting a look at Nov. month end figures for the GM stores. GM brands represent about 11% of Sonic's dealership sales revenues (YTD through Sept.) so the impact would be affected by the limited exposure sonic has to GM.
Also, Sonic admitted that the poor domestic brand sales from last quarter were a result of management at the dealership level and poor merchandise mix (translation: fewer new cars in inventory for customers to choose from due to aggressive inventory control). If they haven't fixed these issues then GM's increase may not have a big impact.
The car biz is fickle though, up one month - down the next