After three months as the nation's most valuable automaker, a bad week in an otherwise stellar year has knocked Tesla from the top perch as the nation's most valuable automaker. Tesla's growth remains stellar, with shares soaring close to 50 per cent this year, twice that at General Motors Co., which retook the spot. Ford Motor Co. has actually fallen in value this year. But a trifecta of bad news in recent days, starting with a tweet from Tesla CEO Elon Musk, has delivered the worst week for the electric automaker's stock since early 2016. Shares fell 4 per cent in midday trading, pushing shares down more than 13 per cent for the week. Musk sent out tweet saying that the Palo Alto, California, company anticipates production of 20,000 Model 3 cars per month in December, which was below previous estimates. Tesla also said that it delivered about 22,000 vehicles in the second quarter, bringing first-half deliveries to about 47,100. That's at the low end of the company's projections earlier this year of between 47,000 and 50,000 deliveries.