I have a 2020 GMC Sierra 2500 CCSB with the 6.6 gasser. (six speed trans, 3.73 rear) I pull a Airstream Flying Cloud 28 foot trailer. The trailer was weighted on a CAT scale, ready for the road at 7,000 pounds. Towing I get 10-11 mpg, with reg.gas, over varied terrain, covering over 5,000 miles. I am very happy with the performance of the gas engine. Plenty of power. My previous truck was a 2011 GMC Duramax diesel. comparing the two, the diesel definitely pulls stronger and got 12-13 mpg pulling the same Airstream. I went to gas mainly because I couldnt take the problems of the diesel emissions anymore, and saved $10,000 going with a gas engine. Can buy a lot of fuel for $10,000 I would buy the 6.6 gas engine again. empty 15-16 mpg. If I get on the interstate and baby it I can get 17 mpg hope that helps