New York Finding the next Tesla among electric vehicle stocks is proving to be difficult.A number of upstart electric vehicle makers' stock prices soared in recent years, as investors looked for the next company to shake up the car market. But all have struggled recently -- as has Tesla itself.Rivian was briefly the third-most-valuable automaker on the planet, behind only Tesla and Toyota, despite having yet to report any sales when it went public. When it finally reported its first sales on De