Ford teased the upcoming Shelby GT500’s engine and confirmed its debut; startup Rivian debuted the R1T and R1S electric pickup and SUV concepts; Jeep revealed the 2020 Gladiator pickup truck. It’s the Week in Reverse, right here at Motor Authority. Ford not only confirmed the 2020 Shelby Mustang GT500 will make its grand debut at the 2019 North…