The automaker says it is adding the shift in response to demand for heavy-duty pickups. The shift will start in the third quarter.
GM will fill the shift by recalling laid off workers who will start arriving in the second quarter. It expects to hire no new employees.
The Flint factory currently runs two production shifts and employs about 2,100 hourly and salaried workers. It made 115,000 trucks last year.
Mark Reuss, president of GM North America, says the move "brings jobs and a needed economic boost to the Flint area."
