The nationwide gas price average broke through $4 a gallon overnight, with diesel just shy of $5.50. So production of HD pickups, the thirstiest of the mass market models, is slowing down, right? Not at General Motors. The General has just added an entire day of production to one plant that builds the beefiest GMC Sierra and Chevrolet Silverado HD trucks, according to a new report. That's an extra 20%, or around 1,100 trucks per day. Everybody's Working Through The Weekend Chevrolet Flint Assembly, in Flint, Michigan, will move to six days a week in June, the Wall Street Journal reports. The plant currently runs three shifts, five days a week, pumping out 2500 and 3500 series GM trucks. "General Motors is making strategic adjustments to Flint Assembly’s production schedule to align with strong customer demand," a GM spokesperson told WSJ.This move isn't a tariff-dodge to take away production from other sites, either. Or at least not directly. WSJ reports a GM spokesperson said this move won't affect GM's plant in Oshawa, Ontario, which also builds the Silverado HD. That plant was cut back to two shifts in January, with GM already moving as much production to the US as possible.According to the report, higher gas prices haven't had an impact on full-sized sales at GM. The automaker said that it has more demand than supply of models like the Cadillac Escalade and some of its full-sized trucks. Paul Jacobson, GM CFO, said that it usually takes four to six months of sustained high prices before buyers consider vehicles with better fuel economy or a smaller size. Big Trucks Are Hot Jay Traugott / CarBuzz / Valnet Last year, GM reported strong growth in pickup truck sales. Its Silverado and Sierra posted their best year in 20 years, with a 7% increase from the year before. Much of that growth came from the HD line, the 2500 and 3500 models, with Silverado posting a 12.2% HD gain vs 1.2% for light-duty and GMC notching a 9.2% increase vs 7.1.Flint and Oshawa are the only two plants that build the HD trucks, though only Flint builds the GMC models. The Flint plant has been running at maximum capacity for quite some time, justifying the capacity increase.Early sales data suggests that 2026 will be a rough year for automakers. Across the board, new vehicle sales are projected to be down 2.6% from last year. HD trucks are some of the most profitable vehicles the Detroit Three sell, with high margins from the big-sellers. If other models fall into loss territory, then these big trucks will help bring the balance sheet back into the black.