Maybe you guys can help me with this?

My truck consistantly gets better mileage commuting to work than driving solo on the highway??? All mileage hand calculated. I run tow/haul all the time. The few times I have run it in regular mode my commute mileage dropped by 1.5 mpg.

My commute is 80 miles per day, 60% driving highway with cruise set at 65-68 mph, and the other 40% is city driving with combination stop go and and runs up to 50 mph between red lights. 17.5 mpg

When driving solo on the highway I set the cruise for 65-68 mph. 15.5-16 mpg.

Otherwise everything else is the same. I run 70 psi in the front tires and 60 psi in the rear. I have a brush guard on the front, a wrap around pipe rear bumper and a 5th wheel hitch in the bed.

Any thoughts? My previous truck (2500hd Duramax Allison) got worse mileage on the commute and better highway mileage. Normally 16 commute and 18.5 highway.