The channel strategy allows for other combinations in smaller markets. And GM officials say that some dealers may be able to survive as single-brand division stores.
But the scenario has left many dealers taking a hard look at their future. Jim Muir, owner of Jim Muir Oldsmobile-GMC in Sterling Heights, Mich., says he will try to survive as a stand-alone GMC dealer.
Muir said he sold about 400 Oldsmobiles and about 550 GMC trucks last year. But short supplies of the most popular trucks - especially Sierras with extended cabs, heavy-duty capability or diesels - pose a problem.
"I have just had some conversation with GM about its inability or unwillingness to give me more trucks," he said.
Muir says he is "paying stupid money" to buy GMC trucks from other dealers and selling them at thin margins to build his customer base.
Jim Lupient, owner of Jim Lupient Oldsmobile-GMC Truck in Golden Valley, Minn., sold 1,500 GMC trucks last year. Even with that volume, he says, he can't support his 80,000-square-foot dealership on GMC alone.
"It can't support that kind of square footage," Lupient said. "If you had something around 25,000 square feet, I think you'd do pretty well."
The logical solution is to combine with a nearby Pontiac-Buick dealer, he said. But neither he nor the other dealer wants to sell.
"I've been here 35 years, and I'd like to remain in the business," Lupient said. "We're just at an impasse."
Even moving to become a stand-alone Chevrolet dealer is a difficult proposition, according to Alan Starling, owner of Holiday Chevrolet- Oldsmobile in St. Cloud, Fla. Starling's store sells about 200 Oldsmobiles and up to 700 Chevrolets in a normal year.
Though the Oldsmobile business might seem secondary, Oldsmobile buyers produced a significant chunk of Starling's service, finance and insurance profits.
"My challenge is to take an existing business model and convert it to a Chevrolet stand-alone facility, which we think is doable," Starling said. "It's not what I would like to do. I don't have much choice at this point."