United States, June 12 -- General Motors announced plans to invest about $4 billion over the next two years in its domestic manufacturing plants to increase U.S. production of both gas and electric vehicles.The new investment will give GM the ability to assemble more than two million vehicles per year in the U.S. This announcement comes on the heels of the company's recently announced plan to invest $888 million in the Tonawanda Propulsion plant near Buffalo, New York to support GM's next-generation V-8 engine.Plants in Michigan, Kansas, and Tennessee will expand finished vehicle production of several of GM's most popular vehicles:Orion Assembly, Orion Township, Michigan: GM will begin production of gas-powered full-size SUVs and light duty...