In 1920, General Motors was a company in trouble. Its founder was fired- for a second time. Henry Ford was eating G.M.'s lunch with his Model T. But a decade later, G.M. had revamped itself into the model of a big business, and would remain so for decades, largely following the same playbook written by Alfred P. Sloan, Jr. in the 1920s. We'll follow its resurgence with help from Paul Lienert, a veteran auto writer and Detroit correspondent for Reuters.