2015 2500 St Tradesman 4x4 Quad Cab, Camper shell, 6 speed manual G56 stick, K&N air filter. Bought used Omaha, drove to Los Angeles 24.1 mpg. Up & down California 6 times in 5 weeks. 10,000 miles (27k to 37k). 8800lbs stock chrome 18" steel rims, 275-70-18 Firestone tires. Avg city 17-21mpg. Freeway 22-28mpg. Is something wrong? I been driving stick since 1970s. Drove 2hrs + 6hrs + 2hts off road in 1st & 2nd 4H in California’s Kern mountains 3000-8500 ft. Elevation & got 15-16mpg? Something was wrong per my landlord neighbors! Great ride in Air Con shopping land & mountain cabins. Changed all filters and all fluids except power steering and radiator and Brake fluids and clutch fluid. Kern County, Bakersfield Dealer said 1% of all trucks get a G56 6 speed manual. He said this trans is the same as the Dodge Viper! Fleet mgr said that the 24mpg is normal & that the automatic transmission sucks 5mpg to run correctly.