High gasoline prices are beginning to weigh on sales of the full-size pickups and sport utility vehicles that generate the most profit for automakers, while hybrids and midsize vehicles gain ground. General Motors said Chevrolet Silverado sales rose 3% in the third quarter from a year earlier, but the increase came from its light-duty version as heavy-duty Silverado sales declined. Suburban sales also fell, contributing to a 6% decline across all G.M. vehicles. Buyers instead favored smaller, less expensive models such as the Chevrolet Trailblazer and Trax. Stellantis reported a 73% increase in light-duty Ram pickup sales, while heavy-duty truck sales fell 6%; a newly introduced hybrid Jeep Cherokee also sold well. Analysts caution that it is too soon to conclude higher fuel prices have fundamentally changed American preferences, as many consumers are driving less or reducing other spending instead of buying smaller vehicles.