The fourth generation of the Ford Thunderbird is a large personal luxury car produced by Ford for the 1964 to 1966 model years.
 This generation of the Thunderbird was restyled in favor of a more squared-off, "formal" look.
 The Thunderbird's sporty image had by that time become only that: the standard 390-cubic-inch 300 bhp V8 engine needed nearly 11 seconds to push the heavy T-bird to 60 mph (96 km/h).
 The softly sprung suspension allowed considerable body lean, wallow, and float on curves and bumps.
 Contemporary testers felt that the Buick Riviera and Pontiac Grand Prix were substantially more roadworthy cars, but the Thunderbird retained its leading market share.
The seventh generation of the Ford Thunderbird is a personal luxury car built by Ford from the 1977 to the 1979 model years.
 In a key marketing shift for Ford, the Thunderbird changed market segments for 1977, shifting from a full-size car to the larger end of the intermediate segment.
 Based upon the Ford LTD II, this generation is the first of four generations of the Thunderbird to share its basic design with the Mercury Cougar.
The Oldsmobile Toronado is a personal luxury car produced by the Oldsmobile division of General Motors from 1966 to 1992.
 Designed to transcend Ford Thunderbird and GM's own Buick Riviera, with its all new transaxle version of GM's Turbohydramatic transmission the Toronado is historically significant as the first U.S.-produced front-wheel drive automobile since the demise of the Cord in 1937.
Wayne K. Cherry (born 1937) is an American car designer educated at Art Center College of Design and employed by General Motors from 1962 through 2004, retiring as Vice President of Design.
 Cherry worked for General Motors in the United States from 1962 until 1965, when he moved to the United Kingdom to take a position with General Motors' Vauxhall Motors subsidiary, becoming Design Director at Vauxhall in 1975.
 In 1983 General Motors consolidated all European passenger car design under Cherry and made him Design Director at General Motors' Adam Opel AG subsidiary.
 Cherry returned to the United States in 1991 and in 1992 became General Motors Vice President of Design.
 Cherry retired from General Motors in 2004.
The fifth generation of the Ford Thunderbird is a large personal luxury car that was produced by Ford for the 1967 to 1971 model years.
 This fifth generation saw the second major change of direction for the Thunderbird.
 The Thunderbird had fundamentally remained the same in concept through 1966, even though the styling had been updated twice.
 The introduction of the Ford Mustang in early 1964 had, however, challenged the Thunderbird's market positioning.
 It, like the Thunderbird, was a small, two-door, four-seater with sporting pretensions, but it was more affordable.
 The Thunderbird's sales suffered.
 Ford's response was to move the Thunderbird upmarket.
Chevrolet ( ), colloquially referred to as Chevy and formally the Chevrolet Division of General Motors Company, is an American automobile division of the American manufacturer General Motors (GM).
 Louis Chevrolet and ousted General Motors founder William C. Durant started the company on November 3, 1911 as the Chevrolet Motor Car Company.
 Durant used the Chevrolet Motor Car Company to acquire a controlling stake in General Motors with a reverse merger occurring on May 2, 1918 and propelled himself back to the GM presidency.
 After Durant's second ousting in 1919, Alfred Sloan, with his maxim "a car for every purse and purpose," would pick the Chevrolet brand to become the volume leader in the General Motors family, selling mainstream vehicles to compete with Henry Ford's Model T in 1919 and overtaking Ford as the best-selling car in the United States by 1929.
The General Motors EV1 was an electric car produced and leased by General Motors from 1996 to 1999.
 It was the first mass-produced and purpose-designed electric vehicle of the modern era from a major automaker, the first GM car designed to be an electric vehicle from the outset along with being the first and only passenger car to be marketed under the corporate General Motors (GM) name instead of being branded under one of its divisions.
The eleventh generation of the Ford Thunderbird is a personal luxury car that was produced by Ford for the 2001 to 2005 model years.
 It was based on the Ford DEW platform.
 Although it was initially well received by the automotive press, garnering accolades such as the "Motor Trend" Car of the Year and a nomination for the North American Car of the Year in its first year of existence, many publications regarded the Thunderbird's revival rather more frostily after a few years; it garnered a place on "Car and Driver" magazine's 2009 list of "The 10 Most Embarrassing Award Winners in Automotive History".
The tenth generation of the Ford Thunderbird is a personal luxury car that was produced by Ford for the 1989 to 1997 model years.
 On December 26, 1988 a completely redesigned Thunderbird was introduced as a 1989 model alongside its sister car, the Mercury Cougar.
 Developed on Ford's new MN12 (Mid-Size North American Project 12) platform, the new Thunderbird featured a more aerodynamic body that was slightly shorter in overall length relative to the 1988 Thunderbird but had a nine-inch-longer wheelbase.
The Grand Prix was a line of automobiles produced by the Pontiac Division of General Motors from 1962 through 2002.
 First introduced as part of Pontiac's full-size car model offering for the 1962 model year, the marque varied repeatedly in size, luxury, and performance during its lifespan.
 Among the changes were positioning in the personal luxury car market segment and mid-size car offering from the 2nd generation to the 5th generation for the sedan and from the 2nd generation to the 6th generation from the coupe; it returned to a full-size car from the 6th generation to the 7th generation for the sedan, positioned below the larger Bonneville in Pontiac's model lineup.

Question: What vehicle produced by General Motors from 1962 to 2002 did testers feel was a more roadworthy car as compared to the Ford Thunderbird?
Answer: Pontiac Grand Prix