SANTA MONICA, Calif. — TrueCar.com’s Performance Scorecards report for automotive manufacturers and brands ranked GM, Porsche and Hyundai as the highest scoring manufacturers on the list for June.

Saab and Mazda were closer to the bottom of the manufacturer list, the report indicated. The brands that received the highest grades were Chevrolet, Audi and Porsche and the brands with the lowest grades were Saab, Mazda, and Chrysler and Infiniti.

The report grades each manufacturer and brand on eight different measurements including pricing, sales, incentives, customer loyalty, market share and days in inventory data.

"General Motors had a great sales month in June and a big drop in their discounts, which propelled them to have the highest grade," said Jesse Toprak, vice president of industry trends and insights at TrueCar.com. "The Japanese automakers continued to be on the bottom of the scorecards due to low inventory, leading to low retail sales change and a decrease in market share change."

The biggest gainers among manufacturers from May 2011 to June 2011 were GM, which moved from an A- to an A+, and Volkswagen, which moved from a B to an A. The biggest decliners among manufacturers during the same period were Jaguar, which moved from a B+ to a C+, and BMW, which moved from an A to a B+.