Odd milage

[toomanytoys]

I towed a 5700lb trailer 300 miles last week at about 70mph and got 11 mpg. Coming back with no trailer at 70 got me 13. I dont understand this. Should be higher without a trailer no?

 

[KWT2000]

there are so many factors that affect fuel mileage direction, wind, temp, fatigue, different fuel from different stations soo it may be just right i go through this with my semi all the time