 Shares of Southwest Gas Holdings Inc. SWX, -0.81 sank 8.4 in premarket trading Wednesday, after the Nevada-based gas and electric utility determined that the best way to maximize shareholder value is not to sell the company, but to continue to execute its strategic plan. The company said it will also advance the process to maximize the value of its Centuri and MountainWest assets through a sale or spinoff. 