Mills won his class in the Rolex 24, which is considered the most prestigious endurance race in the U.S.
He then racked up three second-place, two third-place, one fourth-place and two-fifth place finishes while competing against top international Grand Prix road-racing drivers at tracks in the U.S. and Canada, he said.
Mills trailed former teammate Andy McNeil by eight points going into the final weekend of the series, but a second-place finish in the ninth race put Mills one point ahead of McNeil, he said.
Mills' skills, a top-notch race car and a transmission blow-out on McNeil's team's car gave the local driver the edge he needed to win the 10th race. He won the series by five points.
"I had my fun winning the Rolex 24. When you're first or second in a championship race, it takes a lot of the fun out of racing," Mills said. "It was more mental stress than I'm prepared to deal with these days."
He taxed his mind and body to negotiate the left and right turns, elevation changes, inclement weather, darkness and duration of road-racing circuits.
"The greatest fatigue factor, other than heat, is the mental part of driving," Mills said. "It takes an ungodly amount of concentration to drive a race car."
Mills processed visual information at more than 200 mph.
He memorized track layouts and replayed racing scenarios over and over again in his mind to help him anticipate such factors as where to drive if confronted by spun-out cars on the other side of blind curves, he said.
He stuffed ice packs into the torso of his racing suit to help him deal with temperatures of up to 150 degrees in the cockpit.
He provided feedback to his car's engineers so improvements could be made to extract the maximum from the race car's body design, engine, tires, brakes, suspension and other components, he said.
Mills sometimes shifted gears 30 times during a single lap - sometimes without a clutch, just pumping the brakes, said his wife, Beth Beckner-Mills.
He once spun-out on a tight turn when his new tires were too cold to stick to the early morning race track, and cracked several ribs when his car's steering link broke while speeding downhill and through a fast corner, Mills said.
Such uncontrollable factors "are the things that scare you, looking back on them before the next race," he said.
Mills often braked to about 30 mph from top speeds of more than 200 mph, he said.
"You have to trick your mind in order to do that," Mills said.
And be very experienced.
Mills, whose racing career spans nearly 30 years, said it takes extensive training to obtain the international driver's license needed to compete in the road-racing circuit.
A veteran of more than 100 Grand Prix-style road races, Mills has competed in the Sports Car Club of America (SCCA) Trans-Am road racing series and the International Motor Sports Association GT series.
His appreciation for the engineering aspect of racing grew during his 20-year career at Fairchild Industries, where he served as director of technical development.
In 1999, he was offered the chance to work with General Motors to help develop the Corvette for endurance racing. Mills got back into the driver's seat for that project - and stayed there all the way to the winner's circle at Watkins Glen.
In February, he will defend his Rolex 24 title in Daytona.
He said he won't compete in next season's Grand American Road Racing Series, but this race car driver has been known to change gears - especially when it comes to retirement.