DETROIT — General Motors is adding a twist to the fight for supremacy in the red-hot U.S. pickup market: It’s raising prices.GM is adding almost $2,100 to the sticker price of the base 2014 Chevrolet Silverado. That’s 8.5 percent above the price when the truck hit showrooms in the spring. Other versions of the Silverado, as well as the GMC Sierra, will see similar percentage increases. Raising prices sounds like an odd way to boost sales. But industry analysts suspect it’s a marketing ploy. They expect GM to raise incentives starting next month so dealers can advertise big discounts. Customers will feel they’re getting a deal — whether they do depends on the size of the discount.The move comes after GM’s pickup sales fell 8 percent in September while its two biggest competitors saw increases. Sales of Ford’s F-series, the bestselling pickups in the U.S., rose 10 percent and Chrysler’s Ram posted an 8 percent increase. The Detroit Three dominate U.S. full-size pickup sales, with 90 percent of the market. The Toyota Tundra and Nissan Titan make up the rest. GM didn’t offer the sweet deals that Ford and Chrysler did last month, said Jesse Toprak, an analyst for the TrueCar.com auto-pricing website. Raising prices and then adding incentives is common in the business. And truck buyers especially like to get deals, Toprak said. “This whole change in pricing strategy for trucks at GM is really meant predominantly as a sales-closing tactic for dealerships,” he said. The increase covers trucks built after Oct. 7, so pickups now on dealer lots aren’t affected. GM officials may also be counting on a recent change in buying habits: Consumers now pay less attention to the sticker price. Toprak says most buyers research their cars and trucks online before buying. Many third-party auto websites suggest prices that people should pay that are below the sticker price, he said. “Savvy customers know how to look beyond this and go to net pricing,” he said. In May, Nissan Motor Co. took the opposite strategy. The Japanese automaker cut prices and incentives so its cars showed up in Internet searches done by price-sensitive buyers. Nissan sales are up 13 percent since then. GM spokesman Jim Cain wouldn’t comment on whether the company will increase discounts when its current incentives expire Oct. 31. But he said incentives do give dealers flexibility to promote sales, allowing cash-strapped customers to use rebates as down payments.