At a gala ceremony in the heart of the citys downtown, Detroits civic and business leaders unveiled a new half-ton, 400-horsepower Motown singer Thursday that promises safety, reliability, and soulful, unmistakable melodies. This fully loaded 1,000-pound tenor with deep gospel roots is what Detroit does best, said Alliance of Automobile Manufacturers president Mitch Bainwol, showing off the performers rugged, road-ready construction and rhythm section with optional funk features. Its a dual-exhaust harmonizing machine with full horn accompaniment and superior torque-handling ability guaranteed to churn out dazzling radio singles as well as the occasional politicized street anthem. At press time, the hybrid-electric singers first attempts in the studio had been postponed until engineers can fix whatever is making that rattling noise. 