DETROIT (AP) — People want small cars that get great gas mileage. General Motors Corp. is known for making top-notch trucks and sport utility vehicles. The company’s survival now hinges on the difficult task of convincing buyers that its upgraded cars are just as good as its trucks and worth some extra cash. That’s essentially the business plan for the reconstituted GM. Yes, the plan still includes selling a lot of pickups and SUVs, but nowhere near the volume of past years when GM could count on pocketing upward of $10,000 on every big vehicle. Instead, the revenue to sustain the nearly century-old industrial giant will have to come from cars, which have typically made only hundreds of dollars in profits. Better cars, and lots of them. The change has come quickly. Faced with high gas prices and a weak economy, GM’s sales fell 16 percent for the first half of the year, with trucks off 21 percent and cars down nearly 9 percent.