cars are in motion. and speaking of cars, general motors just reported its largest profit ever. two years after the automaker nearly collapsed. last year's profit was more than $7.5 billion. abc's david muir went to suburban detroit, where the assembly lines are busy yet again. >> reporter: it was an unthinkable headline just two years ago, but gm is celebrating its biggest profits ever. that $7.6 billion beating the last record set nearly 15 years ago. 640,000 more cars and trucks sold last year than the year before. we were invited into this plant in lake orion, michigan, halted in 2009. >> you make about 800 cars here in this plant every day? >> reporter: they do now, after it sat idle for 18 months. they were all laid off, but they are all back. 2,200 employees. those 800 cars a day. >> how relieved are you? >> if i could jump and touch the