Jeeps were an exception to the trend to V6s, and began offering AMC's , known as "High Torque," straight-sixes as a common engine option in 1972. These engines continued to receive upgrades that were advanced for their time, including the fuel-injected, high-performance AMC Straight-6 engine#4.0 version for the 1987 model-year Cherokee, Wagoneer, and Comanche. In 1988, the engine received higher flowing fuel injectors, raising output to and thus producing more power than some configurations of the Ford 302, Chevrolet 305, and Chrysler 318 V8 engines, and more than any of the Japanese 6-cylinder truck engines, but with comparable or superior fuel efficiency. By 1991, Chrysler was no longer bound by legacy AMC contracts to use engine management systems from Renix and started installing Chrysler computers for the . The 1991 model year also saw the introduction of the in the Jeep Wrangler YJ. In 1993, when the Wagoneer was succeeded by the Grand Cherokee (ZJ), the engine was made the base option. The five millionth was produced in Kenosha, Wisconsin by Chrysler on 15 June 2001, autographed by the assembly workers, and donated to the Rambler Legacy Gallery at the Kenosha History Center. The is regarded as probably one of the best ever Jeep engines and has earned a reputation for its durability. Usage of the AMC 4.0 declined in Jeep vehicles after the Jeep Cherokee (in North America) was replaced by the Liberty in 2002, which featured Chrysler's V6 instead. It declined further after the 2005 introduction of the third generation Jeep Grand Cherokee, which also used the V6. The last application of AMC's straight-six was in the 2006 Jeep Wrangler; for the 2007 model year, the legacy engine was replaced with a V6.