Before the two championships combined, Grand American officials introduced a category for the 2013 season to join the Daytona Prototypes and Grand Touring divisions. The new class, GX, accommodated cars and technologies not currently involved in the Grand Am series. alternative technologies and alternative fuels. Included in this group were turbocharged engines; fuels other than gasoline, such as clean diesels; and hybrid powertrains.

Vehicles eligible for the GX division included:

• Audi TT
• BMW 1 Series
• Chevrolet Cruze
• Ford Focus
• Hyundai Genesis
• Lotus Evora GX
• Mazda with the Skyactiv-D turbo diesel
• Nissan 370Z
• Nissan Altima
• Porsche Cayman
• Scion FR-S
• Subaru BRZ
• Volkswagen EOS

One of the first teams to join the new category was SpeedSource with a Mazda6 powered by Skyactiv-D turbo-diesel.

The first test for the new division came at Daytona International Speedway. Entered were three Mazda6 GX from Freedom Autosport and Yellow Dragon Motorsports. The Mazdas were outpaced by the two fastest Porsches, and it got worse from there; they were all in the garage and out of the race by lap 51. The No. 16 Napleton Porsche shared by Nelson Canache, David Donohue, Shane Lewis, and Jim Norman were the fastest qualifiers and started fifty-first overall. The team grabbed the victory, finishing ten laps ahead of the Bullet Racing Porsche Cayman with drivers James Clay, Darryl O’Young, Dan Rogers, Seth Thomas, and Karl Thomson. Third in the GX category was the No. 38 BGB-prepared Porsche Cayman GX, piloted by Lee Davis, Ryan Eversley, Eric Foss, Jeff Mosing, and John Teece.

The next round was contested at the Circuit of the Americas. There was just a single Porsche entry from BGB. The No. 38 Cayman was shared by Jeff Mosing, Spencer Pumpelly, and Daytona class winner Jim Norman. The team started on the GX pole and took the win. The Mazdas were not as quick as the Porsche. Tom Long and Sylvain Tremblay were running at the finish – albeit four laps behind the winners. A second Mazda retired due to a driveshaft failure. Race three of the 2013 Rolex championship was conducted at Barber Motorsports Park. Norman and Pumpelly collected another victory but were outqualified by the two Mazdas. The fastest were Long and Tremblay, but they retired on lap 51. The runner-up spot was claimed by Joel Miller and Tristan Nunez driving the No. 00 SpeedSource-prepared Mazda6 GX.

Grand Am teams traveled to Road Atlanta for the next event. It was the same three entries, but with different driver pairings. The points leader, Jim Norman, was joined by David Donohue in the No. 38 BGB Porsche Cayman GX. The No. 70 Mazda line-up remained unchanged with Sylvain Tremblay and Tom Long behind the wheel. The No. 00 entry was piloted by Joel Miller and Andrew Carbonell. Once again, the Porsche qualified on the class pole, but it was Miller and Carbonell that earned Mazda's first GX victory. Norman and Donohue finished in the runner-up spot. After a five-week break, teams took to the track at Belle Isle in Detroit. Miller was paired with Tristan Nunez; the combination was the slowest qualifier, but their No. 00 SpeedSource Mazda scored its second consecutive victory. The winners were followed by Pumpelly and Norman. Tremblay and Long failed to finish.

The next event was held at the Mid-Ohio Sports Car Course. After many disappointments, Tom Long and Sylvain Tremblay would start from the pole and grab their first victory in the No. 70 Mazda6 GX. Finishing on the same lap as the winners were Spencer Pumpelly and the points leader, Jim Norman. The last round’s victors, Joel Miller and Tristan Nunez, retired. Watkins Glen International marked the second half of the season. Tom Long and Sylain Tremblay were joined by the Road Atlanta winner, Andrew Carbonell, in the No. 70 SpeedSource Mazda 6. Japanese driver, Yojiro Terada, shared the No. 00 Mazda with Joel Miller and Tristan Nunez. The BGB team consisted of the regular duo of Norman and Pumpelly. They started second in class but recorded their first DNF of the year. The trio of Terada, Miller, and Nunez was victorious.

The usual suspects were entered at the Indianapolis Grand Prix Circuit. Sylvain Tremblay and Tom Long bounced back from their Watkins Glen disappointment to start on the GX category pole and take the No. 70 SpeedSource Mazda6 to victory circle. Finishing four laps behind the winners was the Porsche of Jim Norman and Spencer Pumpelly. Despite not delivering the early-season results, Norman still led the driver's point standings. Miller and Nunez finished behind the BGB Motorsports Porsche. Round nine was at Road America Miller, and Nunez was back on form with another victory. However, Norman and Pumpelly finished on the same lap as the leaders, in second place. The result allowed Miller to move within ten markers of the points leader, Norman. Tremblay and Long failed to cross the finish line.

The tenth race of the year was conducted at Kansas Speedway. Joel Miller would take his fifth GX victory of 2013, and Tristan Nunez would become a four-time winner. However, finishing behind them was the Porsche of Jim Norman and Spencer Pumpelly. With these results, the points gap continued to shrink. Bad luck continued to haunt Sylvain Tremblay and Tom Long with another disappointing retirement. The penultimate round of the championship was held at Mazda Raceway Laguna Seca. Joining the series were Scott Dollahite and Jeff Mosing, driving a Lotus Evora GX. They finished third in their debut. Tremblay and Long’s luck turned around with a victory. Once again, it was Norman and Pumpelly in the runner-up position, with Miller and Nunez finishing a distant fourth.

The final race of the 2013 Grand-Am Rolex Sports Car Series was held at Lime Rock Park. Jim Norman won the GX championship after taking his ninth consecutive second-place finish in the No. 38 BGB Motorsports Calcium Pro Porsche Cayman, co-driven by Spencer Pumpelly. Norman opened his campaign with three victories and used consistency to collect the title. At Lime Rock, Tom Long and Sylvain Tremblay took their fourth GX victory in the No. 70 Mazdaspeed / SpeedSource Mazda 6. The Mazda of Tristan Nunez and Joel Miller failed to finish. The Lotus returned and was gridded second, with Bill and Scott Dollahite driving, but crashed on the opening lap.