Hummer, the brand that became synonymous with fuel-guzzling excess, has been reinvented as a planet-friendly electric vehicle.

General Motors this week unveiled the Hummer EV pickup, the first fully electric addition to its line up. But though it doesn’t guzzle a drop of fuel, the excess is still there in the form of an electric powertrain that pushes out astonishing outputs of 750kW and 15,590Nm. That torque figure is not a typo, and it’s generated by three electric motors, which put the power down through all-wheel drive...