General Motors said on Thursday it has tacked on an extra shift to its busy plant in Shanghai, raising monthly capacity by 50% in an effort to meet booming car demand, Reuters reported. The news agency said GM now operates three shifts round the clock to crank out 18,000 vehicles a month, up from 12,000 when the plant ran two shifts, and plans to roll out its new [GM-Daewoo Lacetti-based] Excelle sedan next month.