The programme which began on April is aimed at getting non-GM owners to sample GM vehicles in overnight test drives.
And the carmaker is to put 40,000 vehicles into demo fleets at GM dealerships between now and July 31, when the program ends.
Dealers will have to order additional vehicles during the program to field a full line-up of demos.
GM is requiring participating dealers to have demos on hand for vehicles included in the program and is offering dealers $1,000 discounts per demo.
Dealers are required to have two fleets of demos, one for the first month and the other for the remainder of the program.